Associations Between Exposure to and Expression of Negative Opinions About Human Papillomavirus Vaccines on Social Media: An Observational Study

"Ongoing surveillance of opinions about vaccination on social media may complement surveys and other public health surveillance methods to improve the efficiency and efficacy of public health communication strategies."

This study sought to measure whether exposure to negative opinions about human papillomavirus (HPV) vaccines in Twitter communities is associated with the subsequent expression of negative opinions. To do this, the researchers examined sequences of messages posted on Twitter (tweets) as well as a static view of the social connections between every user who posted a tweet about HPV vaccines in a 6-month period.

As is reported here, the introduction of HPV vaccination was hampered by controversy in some countries. The quality of information available online about the safety and efficacy of HPV vaccines varies, as does the representation of HPV vaccines in the news media. There is some evidence that influence from online media and celebrities can increase vaccine risk perception and rates of vaccination refusal. Given the importance of information sources in influencing vaccination decision making, social media platforms are seen as an opportunity for both the tracking and influencing of vaccination decision making.

Tweets posted by public users were retrieved programmatically via the Application Programming Interface (API) using repeated searches of combinations of the terms human papillomavirus, HPV, vaccine, vaccination, Gardasil, and Cervarix. The researchers also collected metadata associated with the tweets, including the date and time, information about the user, related tweets such as retweets and replies, and the geo-tag (location) information if it was available. For each user who posted one or more tweets about HPV vaccines in the period, the researchers separately used the API to retrieve the lists of users they followed and the users that followed them shortly after the first time they posted a tweet about HPV vaccines during the period. Tweets were classified as negative if they rejected the safety or value of HPV vaccines or promoted refusal.

Between October 2013 and April 2014, the researchers collected 83,551 English-language tweets that included terms related to HPV vaccines and the 957,865 social connections among 30,621 users posting or reposting the tweets. During the 6-month period, 25.13% (20,994) of tweets were classified as negative; among the 30,621 users who tweeted about HPV vaccines, 9,046 (29.54%) were exposed to a majority of negative tweets. These tweets included misinformation, anecdotes, and opinions that may result in vaccine hesitancy or refusal. The likelihood of a user posting a negative tweet after exposure to a majority of negative opinions was 37.78% (2,780/7,361), compared to 10.92% (1,234/11,296) for users who were exposed to a majority of positive and neutral tweets - corresponding to a relative risk of 3.46 (95% confidence interval (CI) 3.25-3.67, P<.001).

The study design precluded conclusions about what proportions of negative opinions expressed in the period were the consequence of exposure (contagion of opinions), the consequence of users creating connections to other users who already hold similar opinions (homophily), or if other external factors caused connected users to express similar opinions. Although this research may be useful for identifying individuals and groups currently at risk of disproportionate exposure to misinformation about HPV vaccines, there is a need for studies capable of determining the factors that affect the formation and adoption of beliefs about public health interventions.

That said, the researchers suggest that "The simple methods...used here may be of practical value for answering questions about how new information becomes established in different communities. For example, do the results of scientific studies demonstrating efficacy tend to spread primarily through scientific communities and not through communities of hesitant parents? Which popular news websites, influential users, or organizations are better connected to communities that are at higher risk of being exposed to, and subsequently affected by, misinformation? How often do young teenagers or their parents pass along negative opinions following encounters with misinformation or negative experiences with the vaccine process? Using new methods for classifying the location and characteristics of Twitter users..., it may be possible to construct Twitter-derived indicators of skewed misinformation exposure in geographic areas and demographic strata, and these may be useful for predicting or reflecting localized shifts in decision making such as increases in refusal. From a practical perspective, this kind of information risk surveillance could be used to complement existing methods for gathering localized information (surveys, interviews, and registry analysis) and improve community engagement and public health actions by targeting resources more efficiently."