Facebook and Twitter Vaccine Sentiment in Response to Measles Outbreaks

"Examination of social media can provide insight into public discussion of vaccination..."

Measles transmission in recent years has been linked to vaccine refusal. A now-retracted study led by Wakefield may have reinvigorated anti-vaccination controversy. Significant media attention to this research and personal anecdotes from celebrities - including on social media - may have caused a sense of fear and distrust in the measles, mumps, and rubella (MMR) vaccine among some individuals, potentially contributing to a decrease in vaccination rates in some locations. This report examines Facebook (FB) and Twitter discussion of vaccination in relation to measles from 2009 to mid-2016, a period including several widely publicised outbreaks in the United States (US).

Social media posts regarding measles vaccination were classified as: (i) pro-vaccination, (ii) expressing vaccine hesitancy (including universal opposition, opposition to contents of selected vaccines or vaccination schedules, or a conviction that vaccine-related injuries occur at higher rates than commonly believed), or (iii) neither (either unclear whether pro-vaccination or hesitant, or irrelevant). Spearman correlations with US Centers for Disease Control and Prevention (CDC)-reported measles cases and differenced-smoothed cumulative case counts over the time period of January 4 2009 to August 27 2016 were reported (using time series bootstrap confidence intervals). A total of 58,078 FB posts (22,331 of which were known to be located in the US) and 82,993 tweets (38,644 tweets known to be in the US) were identified and classified.

For FB, the algorithm classified 22,306 posts as vaccine-hesitant, 17,928 posts as pro-vaccination, and 2,431 posts as uncertain but on topic. It classified 43,259 tweets as vaccine-hesitant, 16,297 tweets as pro-vaccination, and 12,222 tweets as uncertain but on topic. The number and stance of FB posts and tweets classified as expressing vaccine hesitancy or expressing pro-vaccination views are shown in Figures 1 and 2, respectively, within the paper.

Pro-vaccination posts were correlated with the US weekly reported cases: For FB, the odds ratio for a given post being pro versus hesitant during an outbreak was 3.2 compared with a non-outbreak week (95% confidence interval (CI): 1.21 to 6.62); for Twitter, the odds ratio for a given tweet being pro versus hesitant during an outbreak was 4.3 compared with a non-outbreak week (95% CI: 1.28 to 12.2). Vaccine-hesitant posts, however, were uncorrelated with measles cases in the US (FB: 0.01 (95% CI: -0.13 to 0.14), Twitter: 0.0011 (95% CI: -0.12 to 0.12)).

These findings are consistent with a simple view: Many individuals who promote vaccine hesitancy are frequently or continually engaged in online discussions of vaccination, while non-vaccine-hesitant individuals on the whole engage in the debate more so when current events, such as a measles outbreak, bring measles to public awareness. For example, during outbreaks, non-vaccine-hesitant individuals may criticise and blame those who choose not to vaccinate for the outbreak(s) and for putting immunocompromised and vulnerable populations at risk for disease.

These findings may result from more consistent social media engagement by individuals expressing vaccine hesitancy, contrasted with media- or event-driven episodic interest on the part of individuals favouring current policy. The researchers respond by suggesting that "strategies to increase social media engagement by institutions and individuals in favor of vaccination should be developed, urgently. It may be valuable for medical and public health practitioners to ask not only how they may use social media effectively but how they may empower or encourage social media activism by advocates of evidence-based positions (such as vaccination)."