TABLE 1—
Topics Labeled by Vaccine Sentiment and Theme: Twitter, 2014–2017
| Topic Label, Topic No. | % Pro/%Anti | Theme | Amplification |
| Provaccine (>70%) 18 topics | |||
| Antivaccine beliefs are stupid | 100/0 | Criticizing antivaccine | |
| Global philanthropic campaigns | 100/0 | Promotion | |
| Benefits of influenza vaccine | 100/0 | Safe and effective | |
| Promoting vaccine clinics | 100/0 | Promotion | |
| Recommendations for kids and adults | 100/0 | Promotion | |
| Antivaxxers are bad parents | 90/0 | Criticizing antivaccine | Hashtags |
| Philanthropic funding for vaccines | 90/0 | Promotion | |
| Vaccinate to protect others | 90/5 | Safe and effective | |
| Recommendations for students | 85/0 | Promotion | Hashtags |
| Human papillomavirus vaccine reduces cancer | 85/0 | Safe and effective | |
| Expanding UK meningitis vaccine | 85/10 | Provaccine policy | |
| Great moments in vaccine history | 80/0 | Pro-science | |
| Antivaxxers are crazy | 80/5 | Criticizing antivaccine | |
| Nonvaccination spreads disease | 80/15 | Safe and effective | |
| Population impact of vaccines | 75/0 | Safe and effective | |
| Debunking myths about vaccines (provaccine hashtags) | 75/0 | Safe and effective | Hashtags |
| Human papillomavirus vaccine recommendations | 75/0 | Promotion | Hashtags |
| Defending science | 75/0 | Pro-science | |
| Provaccine/neutral (20%–70%), 21 topics | |||
| Philanthropic campaigns for polio | 70/0 | Promotion | |
| Political backlash to antivaccine views | 70/0 | Criticizing antivaccine | Politics |
| Vaccines reduce disease (measles in European Union) | 65/5 | Safe and effective | |
| Influenza vaccine recommendations | 65/10 | Promotion | |
| New Ebola vaccine successes | 60/0 | Safe and effective | |
| Republican primary debate | 60/0 | Criticizing antivaccine | Politics |
| Vaxxed screening debate with DeNiro | 60/10 | Criticizing antivaccine | |
| Tropical diseases campaigns | 55/0 | Promotion | |
| National Immunization Awareness Week | 55/0 | Promotion | Hashtags |
| Support for passing of Senate Bill 277 in California | 55/0 | Provaccine policy | |
| Science to address misperceptions | 55/5 | Pro-science | |
| Unfollowing/blocking antivax | 50/5 | Criticizing antivaccine | |
| Promoting vaccines during pregnancy | 40/0 | Promotion | |
| Blaming antivaxxers for disease | 40/5 | Criticizing antivaccine | |
| Influenza vaccine efficacy | 40/5 | Safe and effective | |
| Opposing “parental rights” arguments | 40/15 | Provaccine policy | |
| Avian influenza vaccine efficacy | 30/5 | Safe and effective | |
| Rejecting alternative schedules | 30/5 | Criticizing antivaccine | |
| Linking outbreaks to unvaccinated | 25/0 | Criticizing antivaccine | |
| Vaccine hesitancy research | 20/0 | Safe and effective | |
| Vaccines 2016 election | 20/15 | Criticizing antivaccine | Politics |
| Both (> 20% each), 9 topics | |||
| Debating parental choice arguments | 70/20 | Criticizing antivaccine/civil liberties | |
| Discussing immune response | 50/20 | Safe and effective/safety concerns | |
| Vaccine mandates | 35/25 | Policy/conspiracy | |
| Other side does not understand science | 35/45 | Pro-science/conspiracy | |
| Debating epidemiological evidence | 30/25 | Criticizing antivaccine/safety concerns | @messages |
| Policy debate on Trump’s views | 25/25 | Safe and effective/civil liberties | Politics, retweets |
| Debating safety and evidence | 25/30 | Safe and effective/safety concerns | @messages |
| Debating school vaccine requirements | 25/35 | Policy/civil liberties | |
| Vaccine harms debate | 25/40 | Safe and effective/safety concerns | @messages |
| Antivaccine/neutral (20%–70%), 9 topics | |||
| Influenza vaccine efficacy and side effects | 0/20 | Safety concerns | |
| Antivaccine “expert” opinions | 0/20 | Conspiracy | |
| Enzyme in vaccines causes cancer | 0/25 | Safety concerns | |
| Safety Commission rumors | 0/25 | Conspiracy | |
| Babies dying after vaccination | 10/25 | Safety concerns | |
| Zika vaccine conspiracy | 5/25 | Conspiracy | |
| Political spam tweets (e.g., #BLM, #Latino) | 0/25 | Civil liberties | Politics, retweets |
| Race-based sterilization in Africa | 5/35 | Conspiracy | |
| Vaccine mandates violate rights | 0/40 | Civil liberties | Politics |
| Antivaccine (75%–100%), 10 topics | |||
| Vaccine industry corruption | 0/75 | Conspiracy | |
| Gates/Clinton conspiracies | 5/75 | Conspiracy | Politics |
| #CDCWhistleblower coverup | 5/80 | Conspiracy | Hashtags |
| Doctor reveals “truth”—found dead | 0/90 | Conspiracy | Retweets, @messages |
| Vaccines cause severe harm (#Vaxxed) | 0/95 | Safety concerns | Retweets |
| Parents of vaccine-injured children | 0/95 | Safety concerns | @messages, retweets, hashtags |
| Environmental toxins | 0/95 | Safety concerns | |
| Vaccines contain disgusting things | 0/95 | Safety concerns | |
| Vaccines cause autism (antivaccine hashtags) | 0/90 | Safety concerns | Hashtags |
| Shaken baby syndrome cover-up | 0/100 | Conspiracy | Retweets, @messages |
Note. Neutral, 33 topics: vaccines in development (8 topics), not English (6 topics), pet or animal vaccines (4 topics), pharmaceutical or technical information (3 topics), jokes or memes (2 topics), and The Vaccines band, general public health, vaccines are painful, Chinese vaccine scandal, news coverage on HPV, pricing for vaccines, links to porn, personal stories, unclear hashtags, vaccine supply chain (1 topic each).