An article titled “A ‘healthy’ doctor died two weeks after getting a COVID-19 vaccine,” suggesting that the COVID-19 vaccine may have been involved in a doctor’s death, was the most viewed link on Facebook in the U.S. in the first three months of 2021.

The article was written by the South Florida Sun Sentinel and republished by the Chicago Tribune.

Fifty-four million U.S. users viewed the post between January and March via the Tribune link.

Crowdtangle, a research tool owned by Facebook, found that the Tribune link was shared by several accounts on the social network, raising ongoing doubts about the COVID-19 vaccine.

Facebook refused to publish the report about the most-viewed posts on its platform from January to March 2021 “because there were key fixes to the system we wanted to make,” Facebook spokesman Andy Stone tweeted Saturday, adding that the article showed “just how difficult it is to define misinformation.”

For more information, read the original story in NPR.