Sentiment, Contents, and Retweets: A Study of Two Vaccine-Related Twitter Datasets.

Introduction: Social media platforms are important channels through which health education about the utility and safety of vaccination is conducted.

Objective: To investigate if tweets with different sentiments toward vaccination and different contents attract different levels of Twitter users' engagement (retweets).

Methods: A stratified random sample (N = 1425) of 142,891 #vaccine tweets (February 4, 2010, to November 10, 2016) was manually coded.