Table 2.

Sentiments of tweets and other social media messages about information or frustration.

Sentiment	Definition	Example (tweet/other social media)
Frustration	Tweet/message contains anger, irritation, contempt, criticism, or source is flabbergasted	“How stupid can you be by not vaccinating your children against measles” (tweet)
Humor/sarcasm	Tweet/message is funny or expresses sarcasm	“HAHAHAHAHAHA. He had drawn red spots on his head and said: ‘oooooh I have measles’” (tweet)
Concern	Tweet/message contains fear, concern, anxiety, worry, or grief about themselves or others	“Around me many vaccinated children with measles. A bit strange and alarming I think. Is there something known about this by the RIVM?” (tweet)
Relief	Tweet/message contains joy, happiness, or relief	“Thank God we are a liberal country (ie, that we have a choice to vaccinate or not)” (other social media)
Question	Tweet/message contains a question or questions for which the user would like to receive an answer	“This you probably know: what happens when you get measles? Do you need treatment or does it go away spontaneously” (tweet)
Minimized risk	Tweet/message minimizes the risk of measles infection and/or the possible complications	“That [ie, measles] was not that severe at all, I have experienced flu disease, which was much more severe” (other social media)
Information	Tweet/message contains information, informative retweets, and/or other information sources about measles	“RIVM expects more measles cases because school holidays are over” (tweet)
Personal experience	Tweet/message contains a personal experience/story about the disease without expressing any concerns	“My daughter has had encephalitis as a complication of an unknown virus infection” (other social media)
Other	Tweet contains none of the above 8 sentiments	“At the left wing also a number of persons are not vaccinating because of other reasons” (other social media)
Information not related to measles outbreak	Tweet has 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)