Table 1.
Topics and subtopics (between parentheses) of tweets, other social media, and online newspapers about the measles outbreak or perceived risks.
| Topic | Definition | Example (tweet, other social media, online newspaper) |
| Measles outbreak (including number of reported measles cases, measles deaths, people experiencing measles, and consequences of measles infection [including hospitalizations]) | Objective information about the measles outbreak | “Number of measles cases has increased to 161” (online newspaper) |
| Refusing vaccination because of religious reasons | Opinions about persons refusing vaccination for religious reasons | “Unbelievable that the love for God can be greater than the love for your own child” (tweet) |
| Critical toward vaccination | Opinions about persons who are critical toward vaccination (eg, Anthroposophists) | “To remember: also followers of Rudolf Steiner (anthroposophical theory) and the Dutch society for conscientious vaccination are very much against vaccination! Also their children are taking a risk at getting measles” (other social media) |
| Perceived risks (including perceived severity of measles disease and not vaccinating against measles, adverse events, effectiveness of measles vaccine) | How public perceives risks of measles disease and measles vaccine | “That [ie, measles] was not that severe at all, I have experienced flu disease, which was much more severe” (other social media) |
| Measles prevention (including additional vaccinations, maternal measles antibodies, obligatory vaccination, vaccinating secretly, vaccinating employees, vaccinating religious people) | Preventive measures taken to control the measles spread | “Young adult without a measles vaccination cannot camp during summer” (tweet) |
| Trust and role institutions (including role of government, role of media, conspiracies) | No trust in information supply, should government interfere in whether people should vaccinate or not, and allegations about production of vaccines and vaccine components | “Subtle lies about measles by the RIVM? Naïveté?” (tweet) |
| Other | If it did not belong to one of the topics above | “What makes that the school exam and a measles infection are similar? Only children are affected!” (tweet) |
| Information not related to measles outbreak | If it had nothing to do with the measles outbreak or a relation with the measles outbreak could not be found | “The mortality of dolphins on the East coast of the USA is caused by a measles-related virus” (tweet) |