Anti-vaccine Messages Research Articles

COVID-19 Vaccine Discourse on Twitter: A Content Analysis of Persuasion Techniques, Sentiment and Mis/Disinformation

This research aims to understand the persuasion techniques used in Twitter posts about COVID-19 vaccines by the different vaccine sentiments (i.e., Pro-Vaccine, Anti-Vaccine, and Neutral) using the Elaboration Likelihood Model, Social judgment Theory, and the Extended Parallel Process Model as theoretical frameworks. A content analysis was conducted on a data set of 1,000 Twitter posts. The corpus of Tweets was examined using the persuasion frameworks; tweets that were identified as emanating from bots were further examined. Results found Anti-Vaccine messages predominantly used Anecdotal stories, Humor/Sarcasm, and Celebrity figures as persuasion techniques, while Pro-Vaccine messages primarily used Information, Celebrity figures, and Participation. Results also showed the Anti-Vaccine messages primarily focused on values related to the categories of Safety, Political/Conspiracy Theories, and Choice. Finally, results revealed Anti-Vaccine messages primarily used Perceived Severity and Perceived Susceptibility, which are fear appeal elements. The findings for messages by bots were comparable to the messages in the larger corpus of tweets. Based on the findings, a response framework—Health Information Persuasion Exploration (HIPE)—is proposed to address mis/disinformation and Anti-Vaccine messaging. The results of this study and the HIPE framework can inform a national COVID-19 vaccine health campaign to increase vaccine adoption.

Characteristics of Antivaccine Messages on Social Media: Systematic Review.

BackgroundSupporters of the antivaccination movement can easily spread information that is not scientifically proven on social media. Therefore, learning more about their posts and activities is instrumental in effectively reacting and responding to the false information they publish, which is aimed at discouraging people from taking vaccines.ObjectiveThis study aims to gather, assess, and synthesize evidence related to the current state of knowledge about antivaccine social media users’ web-based activities.MethodsWe systematically reviewed English-language papers from 3 databases (Scopus, Web of Science, and PubMed). A data extraction form was established, which included authors, year of publication, specific objectives, study design, comparison, and outcomes of significance. We performed an aggregative narrative synthesis of the included studies.ResultsThe search strategy retrieved 731 records in total. After screening for duplicates and eligibility, 18 articles were included in the qualitative synthesis. Although most of the authors analyzed text messages, some of them studied images or videos. In addition, although most of the studies examined vaccines in general, 5 focused specifically on human papillomavirus vaccines, 2 on measles vaccines, and 1 on influenza vaccines. The synthesized studies dealt with the popularity of provaccination and antivaccination content, the style and manner in which messages about vaccines were formulated for the users, a range of topics concerning vaccines (harmful action, limited freedom of choice, and conspiracy theories), and the role and activity of bots in the dissemination of these messages in social media.ConclusionsProponents of the antivaccine movement use a limited number of arguments in their messages; therefore, it is possible to prepare publications clarifying doubts and debunking the most common lies. Public health authorities should continuously monitor social media to quickly find new antivaccine arguments and then create information campaigns for both health professionals and other users.

Human Papillomavirus Vaccine Messaging on TikTok: Social Media Content Analysis.

The human papillomavirus (HPV) vaccine is viewed as a critical tool to protect against six HPV-related cancers. Vaccination is recommended from early adolescence through age 26 years. As young people have become increasingly involved in personal health-related decisions, there is a need to tailor HPV vaccine messaging and reach this priority population on social media and digital outlets. TikTok is a growing social media platform with approximately 70% of its users between the ages of 13 and 24 years. The aim of this study was to understand HPV vaccine messaging and interactions on TikTok as a needed first step to identifying effective strategies to reach young people with important health messaging. Content analysis was performed on 170 top TikToks focused on the HPV vaccine. TikToks were assessed for content, classification type, and number of interactions. Most TikToks were provaccine, while antivaccine TikToks had more user interactions. Cancer and prevention were the main content areas of the analyzed provaccine TikToks, while the side effects were the primary focus of antivaccine messages. Approximately 30% of all top TikToks analyzed were developed by health professionals. TikToks without an explicit vaccine opinion primarily described personal experiences and mentioned side effects most often. TikTok is a growing social media platform that can be used to reach young people and encourage HPV vaccine uptake. Health professionals need to consider the interest that users have in personal experiences and address antivaccine narratives related to side effects.

Immunisation in Byron Shire.

What an unusual series of encounters with Byron Bay ‘Gav’ and his amusingly inconsistent vaccination views.1 This story does highlight some of the key findings from our recent research with a group of non-vaccinating parents in the Byron Shire. The Byron Shire in Northern NSW has about 30 000 residents with a well-established community emphasis on natural health and lifestyle, and a national reputation for lower than average childhood vaccination rates. In 2015–2017 we spoke with 32 parents living in the Byron Shire who had chosen not to vaccinate their children, to understand more about their reasons for this choice. Recent studies with similar aims have also been conducted in well-defined geographical areas near Adelaide and Perth and more recently through nationally targeted recruitment.2, 3 We have learned that parents who make this decision come to it in vastly different ways, that they are in general reasonable, conscientious parents and quite often they review their decision surprisingly frequently.3, 4 Perhaps Gav has reached his views through online conspiratorial reading. However, studies in Australia and internationally convincingly refute the concept that passively reading anti-vaccination messages online or otherwise is the sole cause of vaccine refusal.3, 5 More commonly parents reported such things as an event which caused them to doubt the safety or efficacy of vaccines, mistrust for the institutions who provide and promote vaccination and misalignment with their inherent belief systems and parenting values.3, 4, 6 Despite the path parents take in reaching their decision not to vaccinate, what we have learned is that a nuanced, personalised conversation with non-vaccinating parents is more fruitful than a one-size-fits-all approach. Health professionals' recommendations, when accessible and non-judgemental, have often been highly valued in our studies. They can approach this by asking about parents' stories, making every effort to understand the reasons behind their decision and acknowledging their experiences and concerns. Parents expect health professionals to make a clear, unambiguous recommendation to vaccinate according to the immunisation schedule and appreciate being provided with information addressing their specific questions regarding the safety, efficacy or necessity of recommended vaccines.3, 7 In regards to managing casual conversations in a Byron café, perhaps we need a further research project, for which I (approaching the end of a part-time doctorate) will not be volunteering! There are some great resources for both health professionals and parents including those on the Sharing Knowledge About Immunisation (SKAI) website (https://www.talkingaboutimmunisation.org.au/ and http://providers.talkingaboutimmunisation.org.au/) which has a suite of excellent evidence-based resources to guide effective, respectful conversations with parents about vaccination.8 Gav's story also provides a reminder of the importance of collecting accurate vaccination data. Currently we know the percentages of vaccination coverage throughout Australia; however, since the introduction of No Jab No Pay legislation in 2016, Australia does not record the number of conscientious objections as distinct from incomplete vaccination for other reasons.9 Just as a vet cannot know how many dogs are vaccinated as a percentage of the whole population, only those who present to their practice, Australia no longer has a truly accurate measure of intentional childhood vaccination refusal. One last thing to consider: living in the Byron Shire for over 20 years, I have witnessed a significant cultural change in the past couple of years. As houses are listed for sale, they are snapped up by city dwellers at increasingly impressive prices. This is visibly changing the culture and norms of the area. Perhaps it is timely for us to consider changing our narrative to avoid ongoing ‘anti-vax’ stereotyping of the Byron Shire, steering clear of the risk that we may normalise or even glamorise vaccination rejection as ‘part of the Byron lifestyle’.

Vaccine hesitancy and anti-vaccination in the time of COVID-19: A Google Trends analysis

The COVID-19 pandemic has produced many calls for a vaccine. There is growing concern that vaccine hesitancy and anti-vaccination presence will dampen the uptake of a coronavirus vaccine. There are many cited reasons for vaccine hesitancy. Mercury content, autism association, and vaccine danger have been commonly found in anti-vaccination messages. It is also mused that the reduced disease burden from infectious diseases has paradoxically reduced the perceived requirement for vaccine uptake. Our analysis using Google Trends has shown that throughout the pandemic the search interest in a coronavirus vaccine has increased and remained high throughout. Peaks are found when public declarations are made, the case number increases significantly, or when vaccine breakthroughs are announced. Anti-vaccine searches, in the context of COVID-19, have had a continued and growing presence during the pandemic. Contrary to what some may believe, the burden of coronavirus has not been enough to dissuade anti-vaccine searches entirely.

Analysis of Measles Vaccination Refusal on Social Media (Facebook) among Anti-Vaccine Communities in Indonesia

Measles is one of the main causes of global mortality in the under-fives. The existence of groups that reject immunization caused a decrease in immunization coverage. Anti-vaccine messages are widely delivered on social media. Identification of vaccine rejection behavior can be used as the basis to formulate effective program strategies. The design of this study used rapid assessment procedures (RAP). The informants were from two anti-vaccine communities in the Facebook group. In-depth interviews and observations were done for data collection, and data analysis was performed using the Framework Method. The results found that determinants, such as knowledge, beliefs in health behavior and disease prevention, religion, culture, and government policies play a role in shaping informants’ perceptions of vaccines and disease risks. The design factors of vaccination programs and the reliability of vaccine producing sources were found to be inhibiting factors for informants to receive vaccines. Also, experience with vaccines, health workers' role, and lobbying by anti vaccine groups strengthened informants' attitude who initially doubted vaccines, causing them to reject vaccines ultimately. It is suggested to the Ministry of Health to improve vaccination campaigns through social media, conduct vaccine development study, and increase health workers' knowledge related to vaccines and make their communication techniques more effective.

Understanding the messages and motivation of vaccine hesitant or refusing social media influencers

BackgroundWhile anti-vaccine messages on social media have been studied for content, reach, and effectiveness, less is known about those who create and promote the messages. Online influencers, or ‘everyday people who are influential within their online social networks’, are viewed as trusted voices who are often making similar life decisions as their followers. Therefore, their experiences with and perspectives on health issues can be persuasive. MethodsWe collaborated with a formal network of online influencers to interview, using a semi-structured interview guide, vaccine hesitant influencer mothers about their views on vaccination; their process for developing health-related social media content; their motivation to promote anti-vaccine messages; and their opinions on current vaccination messaging. Prescreening ensured a diverse sample by race/ethnicity, age, education, number of children, and geographic residence. Interviews occurred by telephone, were audio recorded, and transcribed. Themes were generated independently by two coders using a deductive coding approach. ResultsWe interviewed 15 online influencer mothers from across the U.S. (average age 39 years old; all married; 13 Caucasian, 1 African American, 1 Hispanic). In some capacity, 5 of the 15 wrote about vaccination on their blog. Those who chose not to post anti-vaccine content did so for fear of alienating followers or having their platform be the site of combative discourse among readers. When researching their social media posts, the influencers did not trust mainstream sources of health information and relied on alternative sources and search engines.Implications: This exploratory study interviewed influential mothers who have the ability to spread anti-vaccine messages on social media. While most do not contribute to the anti-vaccine sentiment, understanding the motivation and practices of those that do assists the public health community in better understanding the online vaccination communication environment, leading to more effective messages to counterbalance anti-vaccine content on social media.

Detecting Medical Misinformation on Social Media Using Multimodal Deep Learning.

In 2019, outbreaks of vaccine-preventable diseases reached the highest number in the US since 1992. Medical misinformation, such as antivaccine content propagating through social media, is associated with increases in vaccine delay and refusal. Our overall goal is to develop an automatic detector for antivaccine messages to counteract the negative impact that antivaccine messages have on the public health. Very few extant detection systems have considered multimodality of social media posts (images, texts, and hashtags), and instead focus on textual components, despite the rapid growth of photo-sharing applications (e.g., Instagram). As a result, existing systems are not sufficient for detecting antivaccine messages with heavy visual components (e.g., images) posted on these newer platforms. To solve this problem, we propose a deep learning network that leverages both visual and textual information. A new semantic- and task-level attention mechanism was created to help our model to focus on the essential contents of a post that signal antivaccine messages. The proposed model, which consists of three branches, can generate comprehensive fused features for predictions. Moreover, an ensemble method is proposed to further improve the final prediction accuracy. To evaluate the proposed model's performance, a real-world social media dataset that consists of more than 30,000 samples was collected from Instagram between January 2016 and October 2019. Our 30 experiment results demonstrate that the final network achieves above 97% testing accuracy and outperforms other relevant models, demonstrating that it can detect a large amount of antivaccine messages posted daily. The implementation code is available at https://github.com/wzhings/antivaccine_detection.

Dual-process theories to counter the anti-vaccination movement.

Vaccine hesitancy is a problem attracting growing attention and concern. In this paper, we discuss why anti-vaccination messages are influential and which pro-vaccine messages can be effective to address vaccine hesitancy from the perspective of dual-process theories of cognitive functioning. The functioning of the human brain can be characterized by two different types of cognitive functioning: intuitive System 1, which is evolutionarily old, fast, and automatic; and analytical System 2, which is evolutionarily recent, slow, and deliberative. Anti-vaccination messages that inspire fear activate System 1, and vaccine recommendation messages that use statistics activate System 2. System 1 has a greater influence on judgment than System 2. The processing of System 1 is called “trajectory.” Even if adequate knowledge about the effectiveness and safety of vaccination is input to System 2, vaccine hesitancy cannot be easily erased once it is generated by System 1. We suggest that vaccine recommendation messages should target System 1 in addition to System 2, to counter anti-vaccination messages and address vaccine hesitancy.

Analysis of the Anti-Vaccine Movement in Social Networks: A Systematic Review.

The aim of this study was to analyze social networks’ information about the anti-vaccine movement. A systematic review was performed in PubMed, Scopus, CINAHL and CUIDEN databases. The search equations were: “vaccine AND social network” and “vaccine AND (Facebook[title] OR Twitter[title] OR Instagram[title] OR YouTube[title])”. The final sample was n = 12, including only articles published in the last 10 years, in English or Spanish. Social networks are used by the anti-vaccine groups to disseminate their information. To do this, these groups use different methods, including bots and trolls that generate anti-vaccination messages and spread quickly. In addition, the arguments that they use focus on possible harmful effects and the distrust of pharmaceuticals, promoting the use of social networks as a resource for finding health-related information. The anti-vaccine groups are able to use social networks and their resources to increase their number and do so through controversial arguments, such as the economic benefit of pharmaceuticals or personal stories of children to move the population without using reliable or evidence-based content.

Vaccine information seeking on social Q&A services

Experts are concerned about the spread and recalcitrance of vaccine misinformation and its contribution to vaccine hesitancy. Despite this risk, little research attention has been paid to understanding how individuals seek vaccine information online and evaluate its trustworthiness. Here, we hypothesized that when vaccine-hesitant parents seek information about vaccines, they prefer trustworthy sources based on their competence, integrity and benevolence. We explored this issue using 4910 questions and 2583 answers retrieved from two social question-and-answer (Q&A) platforms: “Yahoo! Answers” and the Facebook group “Talking about Vaccines.” We examined what kinds of questions are asked about vaccines, to what extent they are explicitly directed at health professionals or parents, and what features of the answers predict perceived answer quality, based on the theory of epistemic trust. The findings indicate that on different platforms, vaccine-related questions focus on different topics; namely, questions on one platform focused on the risks and benefits of vaccination, whereas they dealt with vaccine schedules on the other. On both platforms, most questions did not specify that an answer should be based on professional expertise or parents' experience. Both pro-vaccine and anti-vaccine answers were proportionately represented among the “best answers”. However, if an answer was written by a health professional, the askers and the community on “Yahoo! Answers” were twice as likely to choose it as the “best answer” to a vaccine-related question, irrespective of whether it encouraged or discouraged vaccination. By contrast, an online experiment revealed that both the identity of the respondent and the stance towards vaccination affected the perceived trustworthiness of the answers. These findings indicate that despite the proliferation of anti-vaccine messages, epistemic trust in mainstream science and medicine is robust. User responses to expert answers suggest that expert outreach in online environments may be an effective intervention to address vaccine hesitancy.

Portrayal of Immunization in American Cinema: 1925 to 2016.

The American media often disseminates antivaccination messages. Cinema in particular reaches many individuals and influences attitudes regarding high-risk behaviors such as smoking and alcohol use. We hypothesized that negative cinematic portrayals of immunization have increased over the last 3 decades. Films released in the United States featuring immunization through 2016 were identified on IMDb and viewed in their entirety by 2 reviewers. Themes were recorded, and the portrayal of immunization (positive, negative, or mixed) across each decade was assessed in a logistic regression model. Cultural references attributed to films (eg, television references) were recorded from the "connection" feature on IMDb. Fifty relevant films were identified (1925-2016). Negative/mixed portrayals of immunization were more frequent after 1990 (odds ratio = 4.0, 95% confidence interval = 1.2-13.5), and films with positive immunization portrayals garnered significantly fewer cultural references than films with negative/mixed portrayals (mean = 9.2 vs 56.2, P = .048). American cinema features increasingly negative portrayals of immunization.

What is in a Google search? A qualitative examination of non-vaxxers’ online search practices

Recent outbreaks of measles cases in the United States have generated concern regarding the developing trend of vaccine hesitancy. While previous research has examined the pro- and anti-vaccination messages that information seekers may produce when searching online, research has not specifically examined how individuals precisely access, search, and evaluate online vaccination information. This qualitative study used semi-structured interviews with 20 parents who chose not to vaccinate their children to examine how parents search online to make decisions regarding vaccinations. Relying primarily on Google as a search engine, parents searched using negative phrases and questions, often demonstrating a confirmation bias throughout the search process. Three themes emerged within evaluation of sources: confirmation seekers, exhaustive seekers, and casual seekers. Evaluation and validation processes varied for each group. Suggestions for the construction of online vaccination messages are discussed.

Viral suspicions: Vaccine hesitancy in the Web 2.0.

A huge and diverse amount of information is available online. In 4 studies, we provided complementary evidence about the psychosocial processes involved in online information gathering about vaccinations and the associated relation with trust in their safety. Study 1 investigated the relation between Italian Google inquiries and vaccine coverage for 0- to 2-year-old Italian children from 2000 and 2015, showing a correlation that turned negative over time. In Study 2, participants randomly assigned to a message providing a dual perspective (false balance condition) endorsed more conspiracy beliefs, which, in turn, reduced trust in vaccines compared with provaccine, antivaccine, and control messages. In Study 3, participants actively selected Google outputs that were in line with their opinion, and this confirmatory bias was particularly strong among participants distrusting vaccination. This association was disrupted by the exposure to provaccine messages, but only if antivaccine alternatives were absent. In Study 4, exposure to online comments questioning the human papilloma virus vaccination influenced attitudes toward the vaccination in a sample of not-yet-vaccinated young women. Practical implications for the way that media cover vaccination topics and for interventions addressing vaccine hesitancy are discussed. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Temporal trends in anti-vaccine discourse on Twitter

Despite vaccination’s role in preventing communicable diseases, misinformation threatens uptake. Social media may disseminate such anti-vaccination messages. We characterized trends in pro- and anti-vaccination discourse on Twitter. All tweets between 2010 and 2019 containing vaccine-related hashtags were identified. Pro- and anti-vaccine tweets and users per quarter (3-months) were tabulated; discussion subcommunities were identified with network analysis. 1,637,712 vaccine-related tweets were identified from 154 pro-vaccine and 125 anti-vaccine hashtags, with 86% of users posting exclusively pro-vaccine and 12% posting exclusively anti-vaccine hashtags. Pro-vaccine tweet volumes are larger than anti-vaccine tweets and consistently increase over time. In contrast, anti-vaccine tweet volumes have decreased since 2014, despite an increasing anti-vaccine user-base. Users infrequently responded across pro/anti-vaccine alignment (0.2%). Despite greater volumes of pro-vaccination discourse in recent years, and the anti-vaccination content userbase being smaller, the anti-vaccine community continues to grow in size. This finding coupled with the minimal inter-communication between communities suggests possible ideological isolation.

Personal stories matter: topic evolution and popularity among pro- and anti-vaccine online articles

People tend to read health articles that have gone viral online. A large portion of online popular vaccine articles are against vaccines, which lead to increased exemption rates and recent outbreaks of vaccine-preventable diseases. Since anti-vaccine articles’ themes and persuasive strategies change fast, their effects on viewers’ behaviors may change over time. This study examined how pro- and anti-vaccine topics and public interests have changed from 2007 to 2017. Computational methods (e.g., topic modeling) were used to analyze 923 online vaccine articles and over 4 million shares, reactions, and comments that they have received on social media. Pro-vaccine messages (PVMs) that used personal stories received the most heated discussion online and pure scientific knowledge received the least attention. PVMs that present vaccine disagreements and limitations were not popular. These findings indicate the importance of narratives and directly attacking opposing arguments in health message design. Anti-vaccine messages (AVMs) that discussed flu shots and government conspiracy received the most attention. Since April 2015, even though more PVMs appeared online, AVMs, especially those about vaccine damage, were increasingly more popular than PVMs. Some social events and disease outbreaks might contribute to the popularity of AVMs. Newly emerged anti-vaccine topics (e.g., false rumors of CDC conspiracy) should be noted. This study shows that certain topics can be more popular online and can potentially reach a larger population. It also reveals the evolution of vaccine-related topics and public’s interest. Findings can help to design effective interventions and develop programs to track and combat misinformation.

An analysis of pro-vaccine and anti-vaccine information on social networks and the internet: Visual and emotional patterns

The communication of information about vaccines and anti-vaccines is analyzed through the monitoring of issuers, news sites, groups, and messages in social networks. We also investigate the effects of information on people’s attention, emotion, and engagement, which were analyzed using eye tracking, galvanic skin response (GSR) and facial expression methods. Results: the flow of communication was not constant, both in the press and on web sites (376 news in 2015, 74 in 2016, 69 in 2017 and, 268 in 2018); posts were informative and neutral; and 80% came from non-professional sources (only 17% were written by a journalist and 3% by a health specialist). On social networks, anti-vaccine Facebook messages and groups were identified, and a mapping of influencers is presented. Analysis of the temporal evolution (years 2015 to 2018) of communicative flows showed that anti-vaccine posts decreased. Gender differences appeared in the visual exploration of information sources and in the provoked emotion responses (GSR and facial expression). In pro-vaccine pages women looked at the headline first, while men looked at the photograph. Emotional responses and engagement did not show differences between anti-vaccine and pro-vaccine web sites. No differences were found in the emotion provoked (GSR) between both website types: anti-vaccination persuasion occurred via cognitive, not emotional, methods by using heuristics (e.g., conspiracy theories). Emotional responses and engagement did not show differences between pro-vaccine and anti-vaccine web sites.

Weaponized Health Communication: Twitter Bots and Russian Trolls Amplify the Vaccine Debate

To understand how Twitter bots and trolls ("bots") promote online health content. We compared bots' to average users' rates of vaccine-relevant messages, which we collected online from July 2014 through September 2017. We estimated the likelihood that users were bots, comparing proportions of polarized and antivaccine tweets across user types. We conducted a content analysis of a Twitter hashtag associated with Russian troll activity. Compared with average users, Russian trolls (χ2(1) = 102.0; P < .001), sophisticated bots (χ2(1) = 28.6; P < .001), and "content polluters" (χ2(1) = 7.0; P < .001) tweeted about vaccination at higher rates. Whereas content polluters posted more antivaccine content (χ2(1) = 11.18; P < .001), Russian trolls amplified both sides. Unidentifiable accounts were more polarized (χ2(1) = 12.1; P < .001) and antivaccine (χ2(1) = 35.9; P < .001). Analysis of the Russian troll hashtag showed that its messages were more political and divisive. Whereas bots that spread malware and unsolicited content disseminated antivaccine messages, Russian trolls promoted discord. Accounts masquerading as legitimate users create false equivalency, eroding public consensus on vaccination. Public Health Implications. Directly confronting vaccine skeptics enables bots to legitimize the vaccine debate. More research is needed to determine how best to combat bot-driven content.

Using Text Mining to Compare Online Pro- and Anti-Vaccine Headlines: Word Usage, Sentiments, and Online Popularity

This study aims to explore differences between health misinformation and true information by comparing word usage, sentiments, and online popularity between pro- and anti-vaccine headlines (PVHs and AVHs). Text mining and sentiment analysis showed that AVHs were more likely to use negative sentiment words and trust-related words. PVHs were more likely to use words related to positive sentiments. Anti-vaccine messages (AVMs) were more popular online than pro-vaccine messages (PVMs). AVMs’ online popularity was not related to its emotion words usage. Among PVMs, those with more positive sentiment words were more likely to be shared, commented on, and reacted to online. Wordclouds and word networks were created to visualize the word usage and clustering. Future directions regarding message design and automatic detection and analysis techniques are provided.

Readability comparison of pro- and anti-HPV-vaccination online messages in Japan

ObjectiveIn Japan, the HPV vaccination rate has sharply fallen to nearly 0% due to a series of sensational media reports of adverse events. Online anti-HPV-vaccination activists often warn readers of the vaccine’s dangers. We aimed to examine distribution and readability of pro-and anti-vaccination online messages with relation to these authors’ professional expertise. MethodsWe conducted online searches via two major search engines. Identified sites were classified as “anti,” “pro,” or “neutral” depending on their claims, and “health professional” or “non-health professional” depending on their authors’ expertise. Readability was determined using a validated measure of Japanese readability. Statistical analysis was conducted using two-way analysis of variance and Tukey’s test. ResultsOf the total 270 sites analyzed, up to 137 (50.7%) were deemed anti- and 101 (37.4%) pro-HPV-vaccination. Of the pro-vaccination sites 71% were written by health professionals. Anti-vaccination messages were found to be considerably easier to read than pro-vaccination ones; both among those by health professionals and non-health professionals. ConclusionOur findings substantiate concern that the anti messages may serve to prolong the HPV vaccination crisis. Practice implicationsWe recommend that health professionals use readability assessment tools and improve the text for easier reading if necessary.