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# Viral Marketing and Exposure to Health and Risk Messages

## Summary and Keywords

In the context of epidemiology, an epidemic is defined as the spread of an infectious disease to a large number of people, in a given population, within a short period of time. When we refer to the marketing field, a message is viral when it is broadly sent and received by the target market through person-to-person transmission. This marketing communication strategy is currently assumed to be an evolution by word of mouth, with the influence of information technologies, and called Viral Marketing. This stated similarity between an epidemic and the viral marketing process is notable yet the critical factors to this communication strategy’s effectiveness remain largely unknown. A literature review specifying some techniques and examples to optimize the use of viral marketing is therefore useful.

Advantages and disadvantages exist to using social networks for the reproduction of viral information. It is very hard to predict whether a campaign becomes viral. However, there are some techniques to improve advertising/marketing communication, which viral campaigns have in common and can be used for producing a better communication campaign overall. It is believed that the mathematical models used in epidemiology could be a good way to model a marketing communication in a specific field. Indeed, an epidemiological model SIR (Susceptible-Infected-Recovered) helps to reveal the effects of a viral marketing strategy. A comparison between the disease parameters and the marketing application, as well as simulations using Matlab software explores the parallelism between a virus and the viral marketing approach.

# Viral Marketing Introduction and History

Over the past 20 years, societies in general have been the subject of several formal and conceptual changes in their economic, social, and political standards as a result of continuous technological innovation that occurs in various fields. It is, according to this reality, that the process of digitization of communications media is assumed to be a significant change mechanism, both in terms of interpersonal relations and marketing communications.

Actually, a coexistence between the online and offline media has been witnessed, which results in a hybridization of languages, strategies, and techniques of communication, translated into the key concepts of interaction and directionality (Lavigne, 2002). Through this relationship, the production and dissemination of information has ceased to belong to the exclusive domain of a single entity to assume a collaborative dimension where all individuals are connected to virtual networks, being able to produce, manipulate, and share content in a direct way (Castells, 2004).

Given the ineffectiveness of traditional promotional communication strategies—from massified and essentially unidirectional nature—communicator entities have responded with new approaches, such as viral marketing, which aims to minimize the resistance of consumers to the promotional messages, thereby establishing a parallelism between the biological process transmission of a virus between individuals in a real context, and the process of transmitting a message from an Internet user to another in a digital context (Nail, 2005).

Viral marketing, in its strategic line, is directly related to the variable promotion of the marketing mix, assuming it is an alternative communication technique, embodied in a dissemination process of promotional content similar to the logic of a viral epidemic. The spread of the message on a large scale is made possible by the collaborative action of individuals in virtual networks (Barichell & Oliveira, 2011). The goal is successfully reached when the message starts to be spread to a relatively small number of initially targeted persons, and then the information is spread as an epidemic to a large fraction of potential consumers (Blaszczyszyn & Gaurav, 2013).

Viral marketing is appealing because it combines the prospect of overcoming consumer resistance with significantly lower costs and fast delivery—especially through technology, such as the Internet (Trusov, Bucklin, & Pauwels, 2009). However, the company no longer has complete control over the marketing message due to this shareability and dynamics process; so this business must become skilled at influencing the message without losing the authenticity of the initial message (Howell, Peters, Thomas, & Robbins, 2012).

Also known as Internet word-of-mouth marketing (Woerdl, Papagiannidis, Bourlakis, & Li, 2008) or word-of-mouth advertising (Phelps, Lewis, Mobilio, Perry, & Raman, 2004), viral marketing has been gaining more and more fans, from professionals to researchers, as an alternative strategy to traditional communication. In this context, a divestment in the traditional media by major advertisers has been observed, and the transfer of funds to the online marketing actions is increasing (Hinz, Skiera, Barrot, & Becker, 2011).

In a general way, it can be presumed that viral marketing is a business strategy that uses existing social networks to promote a product. Its name refers to how consumers spread information about a product with others in their social networks, much in the same way that a virus spreads from one person to another. The basis of viral marketing is in the spread of information by word of mouth, but contemporary information technology has allowed the viral effect to include many Internet-based platforms as well.

This communication technique typically supplies its audience with something of value for free. This can be something as simple as an amusing image, sketch, or game. Whatever the viral content is, it must encourage people to share with others. Viral marketing is useful as a stand-alone marketing communication tool or as part of a larger campaign that uses multiple kinds of communication channels.

According to Kirby and Marsden (2006), the concept of viral marketing has been formalized during the past decade by specialized books, including Malcolm Gladwell’s The Tipping Point, Emanuel Rosen’s Anatomy of Buzz, and Seth Godin’s Unleashing the Ideavirus. The hype about this phenomenon has also been increased by well-known success stories, such as The Blair Witch Project; and the “Subservient Chicken,” by Burger King. The practice of viral marketing in the digital domain has been around for almost a decade and has registered three major stages: in the mid-1990s when digital media started to grow; at the turn of the millennium with the dot.com companies; and nowadays, as advertisers try to stand out from the fragmented media and fragmented audiences.

The origins of viral marketing date back to 1999 when Daniel Myrick and Eduardo Sanchez began drumming up buzz for their now-legendary movie, The Blair Witch Project, using innovative techniques made possible by the relatively new digital culture. The production uses a film structure based on a technique that is made to look like an amateur video shot by real people. The authors capitalized on the realistic look of Blair Witch to build a campaign around it that suggested the footage was actually real: They used a website designed to convince people that the mystery scenario of the movie was an actual missing person’s case. The authors also visited online message boards to spread rumors about the mystery. As a result, on a budget of less than $1 million, The Blair Witch Project grossed nearly$250 million.

As mentioned before, another historic example of viral marketing was the responsibility of Burger King: to promote a new sandwich, they have launched a website that allowed users to give commands to the “subservient chicken,” a man in a chicken costume. When the great majority of people leave websites within eight seconds of visiting, many of Burger King’s 15 million first-week visitors to the “subservient chicken” page spent six minutes or more engaging with the content.

Summarizing, it may be argued that viral marketing is a recent way of approaching markets and communication with customers and can potentially reach a large and fast audience. It exploits existing social networks by encouraging people to share product information and campaigns with their friends, through email or social networks. This type of communication has more impact for the customer because the information is recommended by friends and peer networks instead of standard companies. Marketing campaigns that leverage viral processes of dissemination are widely considered. They have certain advantages over traditional mass media campaigns, especially with the cost effectiveness issues and the ability to reach specific consumer groups.

# Viral Marketing Terminology

Currently there are several perspectives that fit the concept of viral marketing. This terminological uncertainty that has surrounded the concept of viral marketing is based on the speed with which it has been producing technological changes in information and communication systems, prompting major changes in conventional communicative models. Viral marketing corresponds to strategies that encourage individuals to pass marketing messages to each other, resulting in an exponential growth of that message, instead of making a direct product recommendation. Some authors state that viral marketing is the result of amplification of word of mouth through the use of digital media. At the same time, viral advertising creates contagious advertising messages or material that is passed from peer to peer in order to increase brand awareness (Kirby & Marsden, 2006).

According to the authors, consumers no longer use the Internet only for practical purposes, such as research and shopping. The development and adoption of dynamic technologies has generated an increasing demand for online entertainment, which, in turn, gave rise to the production and sharing of content with this goal, while traditional commercial communication efficacy was lost.

The dispersion of meanings is motivated by several reasons: the relative youth of the activity, which causes a lack of terminology acceptation and uniformization; the plurality of used terms by different professionals to define the concepts; the absence of university tradition; and the slow recognition of neologisms by regulators.

It can be assumed that viral marketing is a marketing strategy and tactic aimed at encouraging, somehow, people to talk and to disseminate a product, company, person, or idea of spontaneous order. The message acquires a higher validity and credibility when it is compared with traditional advertising. It lies between mass advertising, free publicity, and word of mouth. The authors call this viral marketing because it spreads and multiplies like a virus.

Some terminologies that contribute to the definition and understanding of conceptual limits are now presented (Petrescu & Korgaonkar, 2011).

• Social media—social interaction based on online media, networking, and information exchange; the content is created by the user and it involves use of the Internet.

• WOM—interpersonal verbal communication (consumer to consumer) is free, and it concerns brands or products; the comments are generated by the users themselves and it requires use of traditional verbal communication.

• Viral Marketing—online and offline marketing activities that aim to influence consumers to pass the marketing message to other consumers; commercial messages created by consumers and it involves use of the Internet.

• Buzz Marketing—interpersonal communication resulting from viral marketing actions; commercial communication generated by the consumer or the advertiser, and it requires the use of traditional media and the Internet.

• eWOM—interpersonal electronic communication (consumer to consumer), alluding to a brand or product; the comments are generated by the consumers and it involves use of the Internet.

• Viral advertising—free sharing of online advertising communication; publicity created by the consumer or advertiser, involving the use of the Internet.

The fundamental distinction between the three emerging techniques in marketing (word of mouth, viral, and buzz) lies in the type of connections used: Word of mouth uses marketing offline connections; viral marketing is based on online connections; and Buzz Marketing takes advantage of both offline as well as online connections, in addition to the traditional media, to generate positive discussions about a company, product, or service.

# Viral Marketing As a Communication Strategy

There are several communication definitions in both the intrapersonal or business context, so always include the concept of verbal and nonverbal communication as a way of sharing information between someone who wants to express an idea and someone who wants to capture it, or what it is intended to capture (Kotler & Armstrong, 2016; Etzel, Walker, & Stanton, 2007). There are some concepts that substantiate the notion of viral marketing, such as the nature of the channels (personal and impersonal); the realization of the communicative effectiveness of the bidirectionality speech when compared with the massified approach of traditional media; and the recognition of the growing influence that an opinion leader may have on consumers through advice and opinions.

## Word-of-Mouth and Buzz Marketing

In this context, Río, Domínguez, and Garrido (2014) clearly value the personal channels, mainly the social ones, where, in the context of organizational communication, several approaches can be used: to identify individuals or companies with influence on the selected target audience; create opinion leaders to promote the use of the product or service; use recognized public figures as testimonial in the ads; Buzz Marketing (also known as rumors); word of mouth; and viral marketing. According to the authors, the concepts of word of mouth and Buzz Marketing contribute to the definition of what is viral marketing. The first one, as a natural consequence, occurs when the information is amplified by communication technologies; the second one is just a way of amplification by the process of face to face, plus comments and rumors.

Buzz Marketing is a viral marketing technique that is focused on maximizing the word-of-mouth potential of a particular campaign or product. This can be potentiated whether the conversations about the product pass from consumers’ families and friends to larger-scale discussions on social media platforms (Boone & Kurtz, 2012). When people talk about the products, brands, or services, companies hope to grow their awareness through the growth of online traffic and increase sales and profits.

In the broad sense, it can be assumed that viral marketing is based on a set of strategies and worth-of-mouth techniques—about a brand, product, or service—that are growing at an exponential rate due to information and communication technologies (Río et al., 2014). These strategies and techniques differ from classical advertising, given that the message is spread by consumers or potential consumers, not by advertisers (Porter & Golan, 2006).

## Viral Marketing versus Traditional Marketing Communication

The world of technology and social media is having a significant impact on how we behave socially, act as consumers, and how we do business. Therefore, companies must have a new mindset when they think about applying their budget to the new era of marketing and communications. There are features that can distinguish viral marketing as applied to digital systems to the traditional marketing features made in the past.

In this context, the brands are transferring to consumers the power to communicate and disseminate their promotional messages along its network of contacts, with a smaller investment and a much higher velocity compared with traditional media, either the Internet or in a mobile context.

However, this process also has risks that the authors highlight (Kaikati & Kaikati, 2004; Phelps et al., 2004; Welker, 2002), as its uncontrollable nature, in particular, loss over content and audience reach, few possibilities exist to measure success and timing. If a marketer has decided to use email as a way to drive traffic to their website, they are competing with other people who are using the same structure, which has the risk of having their message lost among all the other email messages people receive on a daily basis. At the same time, negative word of mouth leads to boycott, ruin, and unfavorable attitudes. Unlike traditional advertising, viral marketing is not an interruptive technique. In this way, a bad campaign could be exposed on the Internet for a long time via peer-to-peer endorsement, and just a few people will take the time to investigate for themselves to figure out whether this negative buzz is warranted. It should be emphasized that some consumers, especially bloggers, are unwilling to provide referrals unless there is some return—which can increase the money spent by the company. It is also important to mention that legal emerging issues have to be considered: Many people have concerns about privacy issues and want to know what the companies they do business with are planning on doing with their personal information, so they may not be interested in participating in a campaign if they think they are providing fodder for spam marketers. Finally, it’s important to realize consumers may feel exploited, cheated, and used, which can lead to an ultimate goal of not using that kind of service or product.

In an attempt to understand what characterizes the behaviors, motivations, and attitudes of those who forward the messages (receiving and passing), in order to influence it, Phelps et al. (2004) created the basis for an explanatory model that contains four stages: stage 1—receipt of the message (identification as a pass-along message with thoughts about proximal and distal senders and also the affective response); stage 2—first decision point (the decision to open or delete de message); stage 3—if opened, the reading and decoding of the message (message structure and message content); stage 4—second decision point (deciding whether to forward the message on to others). Under this model, the authors concluded that the messages that arouse strong emotions (humorous jokes, emotional or sad stories, inspirational content, for example) are more likely to be forwarded.

## Classification of Viral Marketing Campaigns

Kaplan & Haenlein (2010) reports that a viral marketing campaign needs three basic conditions: the right environment, a good message, and the correct people to act as influential messengers. Viral marketing can be a very effective marketing tool and lead to positive results for a brand or company, but if the campaign is negatively oriented, it can lead to a negative effect toward a brand or company. Kaplan and Haenlein (2011) have attempted to introduce a new kind of framework in which four types of viral online marketing campaigns are identified. They classify viral marketing campaigns in four major groups, varying by negative and positive outcomes of social media marketing:

Strokes of Luck are campaigns initiated by consumers with highly positive approaches to product, service, brand, or company; the repercussions are positive in terms of sales volume and reputation; it is positively oriented and distinguishes itself as being created through positive reactions from consumers and is considered a non-strategically planned campaign (the case of the Diet Coke and Mentos experiment is a good case to demonstrate this kind of campaign).

Triumphs are at all similar to the Strokes of Luck and considered a positive campaign, but the initiative comes from the company; a triumph campaign is a positively oriented social media campaign in which a company is capable of creating its own viral success through a strategic marketing campaign; it is considered successful when consumers, whom might have no affiliation with the company, are willing to share the campaign within their Facebook community, through groups and conversations (example given, the case of Burger King’s Whopper Sacrifice campaign).

Nightmares campaigns that are initiated by consumers consist of posting or sharing negative campaigns/comments on social media platforms, with highly negative approaches to product, service, brand, or company; according to some authors, the increased power of consumers on social media, and the raise of bad social behavior on an online platform; this negative behavior is due to no feeling of guilt, the mob of other users to back them up, relative anonymity, and no accountability for their actions on such platforms; the consequences could be deeply negative in terms of sales volume and reputation for a brand or company (example, Valentine’s Day—the case of American low-cost airline JetBlue Airways, where over 131,000 customers affected by the cancellations, delays; in this case, it was necessary to offer varying levels of compensation to try to restore the level of trust in the company).

Homemade Issues distinguishes itself, due to the fact that the companies themselves are the instigators of negative viral marketing; the production or professional should not be overly commercial; the promises and references must be real and not misleading (the case of Charlie’s and Jeremy’s blog Sony PSP is an example of this).

# Viral Marketing Tactics and Practice

The planning stage of a viral marketing campaign should involve setting out feasible objectives, developing the campaign strategy, coming up with a viral idea that can generate buzz, and then developing the copy strategy. If the viral campaign is part of a wider marketing initiative, the planning activity should also help the brand to integrate and amortize media, public relations, and creative development activity (Kirby & Marsden, 2006).

With respect to certain techniques and principles that underpin the effectiveness of viral marketing, there are a number of recommendations that some authors point out. Among companies that use this communication strategy, stand-out examples are companies such as Procter & Gamble, Microsoft, BMW, and Samsung, which take on the viral marketing as a consumer-initiated activity that spreads the marketing message unaltered across the market or segment in a limited period team, mimicking an epidemic (Gardner, Sohn, Seo, & Weaver, 2013).

## What Affects Online Viral Marketing Success?

Studies in this area typically focus their attention on either intermediate actions/processes such as the probability of opening and passing along viral information (e.g., Ho & Dempsey, 2010; Liu-Thompkins, 2012), or emphasize the adopted strategies that a viral campaign used in the promotion of a product (see Bampo, Ewing, Mather, Stewart, & Wallace, 2008; Katona, Zubcsek, & Sarvary, 2011).

In literature, three types of factors have been suggested. The first is related to the message characteristics: the content and creative design of a viral message are the responsibility of the advertiser, and an effective viral message should break or capture the consumer and encourage further pass-along of the message. The second one concerns the individual sender or receiver characteristics that can affect the success of viral messages, namely, consumers’ personality traits, and demographics issues or motivations for sharing content. Finally, the social network characteristics are also important, because they describe the connection between consumers; in this case, a consumer’s role in diffusion depends on the position in the social network, as well as the relationship of the consumer to others.

## Attributes of a Successful Viral Message

As key attributes of a successful viral message, we can highlight features like entertainment, humor, curiosity, surprise, useful information, and relevant content. The more engaging and compelling is the message, the more likely it is to spread successfully through a network of contacts in continuous growth (Dobele et al., 2007). In this respect, the message developers should note that messages that arouse emotions such as humor, fear, and sadness are more likely to be forwarded. According to the findings of these authors, the effectiveness of viral messages also varies by gender: Disgust-based and fear-based campaigns are more likely to be forwarded by male recipients than female recipients, for instance.

According to Dobele, Toleman, and Beverland (2005), there are five characteristics that make a message engaging, or from a practical perspective, that encourage consumers to spread marketing messages: (1) capture the imagination by being fun and intriguing (emotion must be a vital part of a viral marketing campaign); (2) attach to a product that is easy to use or highly visible; (3) be well targeted (the influence of groups and opinion leaders in individual decision making is relevant); (4) are associated with a credible source (must be believable); and (5) combine technologies (mobile, email, social media).

In a study by Phelps et al. (2004), the authors identify 28 reasons for forwarding messages. According to the quantification of the results, we highlight seven, in order of importance: (1) “Because it’s fun”; (2) “Because I enjoy it”; (3) “Because it’s entertaining”; (4) “To help others”; (5) “To have a good time”; (6) “To let others know I care about their feelings”; and (7) “To thank them.” Regarding the contrary action—not forwarding messages—this occurs because message contents are not in line with the quality standards and relevance of Internet users. Apart from these reasons, the authors insist on a basic strategic procedure based on the importance of selecting targets who will find information relevant enough to pass along.

## Groups of Message Transmitters

According to Kaplan and Haenlein (2011), the right people can transmit the right message in the right circumstance. There are three groups of message transmitters: (1) Market mavens (“receivers”)—individuals who have access to information and are motivated to engage in debate to diffuse information to other consumers; (2) Social hubs (“distributors”)—people with a very large social network, they may act as bridges to other connections; and (3) Salespeople (“amplifiers”)—sellers receive a message, make it important and convincing, and pass it on to community centers, creating a facilitator between marketer and consumer.

## Ways of Spreading Viral Content

There are countless ways of spreading viral content. This can be shared through video sharing sites; personal blogs; groups or discussion forums; or simply being sent by email, as a web page hyperlink, or as attached content. Regarding the profile of users that can enhance the spread, there is evidence that Internet users who are more individualistic and/or more altruistic tend to forward more online content than others (Ho & Dempsey, 2010).

According to Berger (2014), there are six essential steps that determine the potential for contagion of products, ideas, and services. The first relates to the social potential, that is, people tend to share something that makes them look good, that valorize them, which distinguishes and makes them feel like pioneers. There is the real conviction that the kind of discussed and shared thematic influences the way that others see your profile. Then the importance of the handles is identified, that is, the need to identify and build the elements that foster an immediate association with the product, service, or idea: The handles are stimuli that lead people to think of related things. The emotions emerge as an element that will increase the contagion potential. We need to talk about the product, service, or idea in a way that generates emotions: When there is emotional involvement, there is an increased of sharing intention, or put another way, when something is interesting it generates sharing.

Being public, offer practical know-how, and telling a story are the three remaining steps. That is, optimize the knowledge of the product, idea, or service in large scale, to make things more observable, facilitate its imitation, which increases the likelihood of becoming popular; create useful information and experiences that motivate sharing, pass on the knowledge and skills for people to easily share; and, finally, to frame the subject of sharing in an engaging narrative, valuable, and able to integrate information in an intuitive way (not explicit), where the message is so embedded in the narrative that the history cannot be counted separately, rather than pure information.

The main consequence of the advertising saturation of traditional media—the percentage of time and space devoted to advertising in relation to the recommended or legal limits—is the lack of visualization and memorization of the messages by the audience (Río et al., 2014).

For a viral marketing action to effectively result, it should facilitate the process of sharing and relaying between users: The greater the ease, the greater the spread of the message. In this context, Gabriel (2010) posits the following recommendations: Publication of information of great interest should always be accompanied by a sharing link; images and/or videos must be downloaded quickly and be compatible with major operating systems; the use of small applications should include a quick, easy, and compatible installation.

## Procedures to Create Viral Content

In the creation and management of a viral marketing action, there is some advice regarding certain procedures (Río et al., 2014), although it considers that some specificities associated with the idea, product, or service will condition its generalization: clearly define the action goals (planning); objectively segment your target audience (qualitative and quantitative); originality and surprise (distinctive creativity); circumscribe the messages of Issuers (each person has a valid average number equal to or less than 150 effective contacts—Dunbar’s number—instead of concentrating on having as many seeds as possible, companies should instead focus on having an infectious message and seeding it to as many subgroups that are disconnected); structure easily memorable and interesting messages (emotionally involve the receiver); click friendly (in terms of readability, download, and relay); offer some sort of compensation to the sender; reward the sender; the message should be free; use support communication actions (usually in offline context).

# An Epidemiological Model to Viral Marketing

## Viral Marketing and Virus

Viruses are biological entities that use the metabolism of the cells that infect to reproduce inside multiple replicas. That is, they necessarily depend on other living cells for reproduction and may exist (Collier & Oxford, 2006). However, they do not exist in this contagion metaphor—biology and marketing—an intention to cause any curse. The viral marketing infection is voluntary and selective, that is, the infected host transmits the message to those it considers likely to be interested in a brand, product, or service: In this case it generates a conversation, which may be supplemented with comments and recommendations and may even motivate creativity with formal variations of the initial message. This reality gives a major role to consumers, turning them into channels and content producers, in contrast to the passivity inherent to traditional communication models. In this sense the effect of this approach is more effective, more pervasive, and much faster than the communication that uses traditional and mass market broadcast media. In fact, one of the reasons for the effectiveness is exactly the targeting capabilities of the message through demographic and qualitative profiles of those who are infected and those who intend to infect—we can assume that there are homogeneous values between friends, coworkers, and eventually relatives.

This analogy between biological viruses (diseases that spread from people to people) and the virus associated to the products, services, or ideas should assume that there is a significant difference, particularly with regard to the expected size of the transmission chain. One person can initiate the spread of a disease, to reach large numbers of people, generating an epidemic. These kinds of long chains, according to Goel, Watts, and Goldstein (2012) are less common: People share products, services, or ideas, but the probability of one person starting a long chain is, admittedly, low.

In viral marketing, the process is initiated by the agents responsible for the infection (advertisers or advertising agencies, for example), which define certain contagion platforms (email, social networks, mobile phones, etc.) to infect the first entities, which can be certain opinion leaders (Berger, 2014). According to the study Psychology of Sharing (cit. in Río et al., 2014), 85% of respondents share information over the Internet because the reaction of others enhances understanding of content, 84% because they feel a real need, 78% because it is one form of social integration, 68% because it is a way to show their tastes to others, and 49% because they want to influence or change the views of others.

## Viral Marketing As Epidemiological Model

When a marketing message goes viral, it is analogous to an epidemic since it involves a person-to-person transmission, spreading within a population. Using insights from epidemiology to describe the spread of viruses, a mathematical model of the viral marketing process is proposed. The main aim of this approach is to develop a set of simulation experiments to explore the influence of several controlled and external factors that could influence viral campaigns (Rodrigues & Fonseca, 2015).

It is presented as an SIR model:

• $S(t)$—susceptible (individuals who can contract the disease);

• $I(t)$—infected (individuals who can transmit the disease);

• $R(t)$—recovered (individuals who have been infected and have recovered).

The analysis of a viral marketing campaign can be explained by a standard epidemic model (Leskovec, Adamic, & Huberman, 2007; Rodrigues, Monteiro, & Torres, 2013; Rodrigues et al., 2014).

These compartments are mutually exclusive, which means that each person can only be in one compartment each time. It is also assumed that the total population is constant, which means that $N=S(t)+I(t)+R(t)$.

To describe the model it is also necessary to present a set of parameters:

• $δ$ contact rate among individuals per period of time;

• $τ$ probability of a contact between a susceptible and an infected that results in disease transmission;

• $β$ infectivity rate;

• $γ$ recovery rate.

The number of infections among the susceptible population in a period of time depends on the constant rate $(δ)$ at a given period and the transmissibility $(τ)$ of the disease given a contact. So, the constant $β=δτ$ is called the infectivity parameter.

The system of differential equations that translates the dynamics of viral marketing is composed by the following:

$Display mathematics$

subject to initial conditions $S(0)=S0,I(0)=I0,R(0)=R0$.

The model provides a simple and intuitive approach, modeling the VM process through an epidemiological point of view, where a disease is spread by person-to-person contact. In the marketing context, a susceptible individual is a potential consumer who may accept the message or use an offering from a company; this compartment is called the target audience. An infected individual passes the message or uses a unique product from the company and/or recommends it. $β$ is the rate of moving from the target audience to infective. The infected individuals start to spread the message through social contacts. When an individual stops to share, a message passes to the recovered compartment (Gardner et al., 2013; Sohn, Gardner, & Weaver, 2013).

These parameters can also be explained in the marketing context. Infectivity is influenced by transmissibility $β$—through the marketer’s efforts to seed the market with the message and the acceptability of the cost in time and effort to pass along the message—and the contact rate $(γ)$ where the extent and the suitability of the social network are key aspects (Gardner et al., 2013; Marutschke & Ogawa, 2014). Here, a target member must perceive the message; has the predisposition to deal with the message; and finally, must be motivated to share it. Factors such as exhausting mailing lists, forgetting, and no interested by this message or divergent attentions can leave the viral marketing campaign. If the exit (recovery) rate is high, the infective recovers rather quickly. Thus, it is important to analyze and to assess the impact of a message to the target audience and the number of members of the target market who have actively shared the message.

Figure 1 shows a simulation with this model, representing the dynamics of the three state variables. It can be observed that the curve of susceptibility is decreasing all over the time, because once infected it never returns to the state of susceptibility; this means that a person receiving the company’s information is aware of the product/service and never becomes naïve; this individual can decide to share information (remaining infected) or not (becoming recovered). The infected curve reaches a peak of beyond the time 10 (minutes, hours, days, weeks, depending of the time scale). This information could be very useful for the business, because the manager could prepare stocks or other kind of services for the next days in order to provide good service for the client. Depending of the flatness of the curve, the response should be adaptive. If the initial number of infected individuals is bigger, the peak is higher and is reached faster. The curve related to the recovered compartment is important because it accumulates the number of individuals that have been exposed to the viral marketing campaign. On the one hand, the marketer could have an idea of what kind of impact the campaign has on the target audience and what could be changed or improved to reach a faster or bigger audience. On the other hand, if the total number of recovered individuals is received in a short period of time, the marketer can rethink the initial investment (used in the initial infected individuals) and save some money and effort for the company.

Click to view larger

Figure 1. Susceptible-infected-recovered model, with the parameters $β=0.25$ and $γ=0.1$, and the initial conditions $S(0)=900,I(0)=100$ and $R(0)=0$.

Changing the parameters values, the shape of the curves could change, and the spread diffusion can be reached in different velocities. It is possible to realize that a high value for infectivity $(β)$ leads to a greater number of target members reached, and the audience is reached faster. However, the increasing of the recovery rate $(γ)$ value leads to a decreasing of sharing the message, because an individual tends to forget or to be not interested in passing the message more quickly.

In an epidemic, we cannot control how many people we have initially infected, before health authorities start specific treatments or apply measures to control the disease. However, in a viral marketing message, we can simulate and predict the effects of a campaign depending on the initial behavior of the people that are infected. One of the challenges of promoting a viral marketing campaign is to know how many people should be initially affected, in order to create a huge diffusion of the product or service, which corresponds in the mathematical model to the increase of the value of $I(0)$. As expected, when the amount of initially infected people is high, the viral campaign reaches its peak more rapidly. However, increasing the seeding directly may require more costs for the company, and sometimes, a big number of initial people infected would likely be very costly in marketing reality, and the results could not be the expected ones, in terms of time of exposure and proportion of people reached (see, for example, Rodrigues & Fonseca, 2016). This model can be understood as a tool to decide what should be the ideal number to start the viral marketing campaign. An interesting example of a viral marketing case study applied to reality can be found in Gonçalves, Rodrigues, and Monteiro (2017).

## Discussion of the Literature

The concept of viral marketing has been discussed in the literature for over 15 years, since Jeffrey Rayport first introduced the term in 1996. However despite the increasing popularity of viral marketing, factors critical to such a new communication medium remain largely unknown. Currently, when we began a reflection on the concept of viralization within business sciences and particularly in marketing, the central issue, as highlighted by Berger (2014), lies in the need to understand why certain products, ideas, or behaviors conquer people to the detriment of others, regardless of their intrinsic characteristics (quality, price, and ease of obtaining) or extrinsic (perception, often resulting from the communication variable). Examples of social epidemics provided by the author range from simple places that have become fashionable venues; products that become star status or behaviors that are widespread in favor of a particular practice; and, consequently, business (such as the recent generalization of running in Portugal and the different business associated with it: products and direct and indirect accessories, food, personal trainers, etc.). Despite this fact and despite the large sums invested in communication and marketing, the number of products and services that become popular by this method is relatively rare.

Viral marketing as a process is often portrayed as a random ground-up phenomenon over which marketers have minor control. However, a more accurate examination makes it possible to identify a number of strategies that can optimize this marketing communication tool. In general, it may be assumed that the concept of viral marketing was introduced in the academic and professional context during the first decade of this century. As already mentioned it arises as a result of the audience immunity to commercial messages resulting from a context of hyperfragmented and overwhelmed marketing communication.

In academic terms there is no real consensus on the soundness of the concept: we have authors that consider the viral marketing a passenger concept as a result of some trendiness (Klopper, 2001). Others, such as Ferguson (2008) attribute it to the importance of fleshing out a paradigm change in the connection and building of relationships between communicator’s entities and consumers, creating concepts as interactivity, participation, and cocreation, leading to a new role assumed by the consumer. At the same time, in a professional context, the number of technicians with training in the area is increasing and as the investment required is not very significant and the results are often impactful, there are the professional approaches that dominate the great majority of the initiatives in the area. As an example of this growing professionalization, we have the creation of institutions such as the Word of Mouth Marketing Association (WOMMA), which since 2004 is dedicated to defining procedures and evaluation metrics of what they refer to as a new discipline.

Despite the earliness of the concept, there are several lines of thinking that have considered different principles when we refer to the effectiveness: authors who appreciated the importance of the focus on opinion leaders (influencers) rather than content (Adamic & Adar, 2005; Kozinets, De Valck, Wojnicki, & Wilner, 2010); authors who only value the creative differentiation of content (Bakshy, Hofman, Mason, & Watts, 2011; Watts, Peretti, & Frumin, 2007); and other authors that classify at the same level the importance of those who send the message and the creative approach (Chiu, Hsieh, Kao, & Lee, 2007). Even regarding the content there is no consensus about the reasons that justify why some communication actions are more viral than others. A study was carried out about contents that has gone viral, in which the New York Times concluded that positive content is more likely to become viral than negative content (Berger & Milkman, 2012). Messages that provoke strong emotions such as humor, fear, sadness, and inspiration are also more likely to be shared (Berger, 2014).

In fact, it was the information and communication technologies that have raised and streamlined the traditional concept of worth of mouth to the more conceptual and contemporary category of viral marketing, particularly through the connection of computers and mobile devices to the Internet, such as tablets and smartphones. With the construction of social networks based on these devices, it became easier to share and recommend commercial content; it also facilitated a peer-to-peer logic, especially chats, forums, instant messaging applications, and blogs, thereby originating a communicative immediacy both synchronously and asynchronously.

Any categorization to be done for the concept under consideration should be assumed as something always in permanent construction, given that viral marketing is a dynamic phenomenon, constantly evolving and formatting (Gîrboveanu & Puiu, 2008). Let’s consider as an example the evolution of the means and platforms: from email, through the text messages from mobile phones (SMS), MySpace since 2003, Facebook since 2004, YouTube in 2005, Twitter in 2006, and Instagram and Pinterest from 2010.

Technology is slowly making a permanent impact into our lives and viral marketing will become an important part of any organization strategy, whatever their dimensions, experienced or unexperienced in the field of social media marketing. The ability to reach the consumer through viral marketing campaigns and possibly build up a relationship between a company and client will, in turn, lead to a larger degree of customer brand engagement.

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