Massive Facebook study on users’ doubt in vaccines finds a small group appears to play a big role in pushing the skepticism

Facebook is conducting a vast behind-the-scenes study of doubts expressed by U.S. users about vaccines, a major project that attempts to probe and teach software to identify the medical attitudes of millions of Americans, according to documents obtained by The Washington Post.

The research is a large-scale attempt to understand the spread of ideas that contribute to vaccine hesitancy, or the act of delaying or refusing a vaccination despite its availability, on social media — a primary source of health information for millions of people. It shows how the company...