Hamlin, a defensive back for the Buffalo Bills, suffered a cardiac arrest during Monday night's high-profile matchup against the Cincinnati Bengals.
On Wednesday he remained in hospital, but
an uncle said he was showing signs of improving. There's been no further information about any underlying causes which could have contributed to his cardiac arrest.
Research by the Center for Countering Digital Hate (CCDH), a non-profit campaign group based in London and Washington, found that mentions of an anti-vaccine film quadrupled after the player's collapse.
CCDH chief executive Imran Ahmed said activists were "cynically exploiting tragedy to baselessly connect any injury or death of a notable person to vaccinations".
The day after the match the documentary Died Suddenly, which was released in November last year, was mentioned nearly 17,000 times, the CCDH says. The BBC
previously looked into the claims in the film and found little or no evidence behind many of them.
Caroline Orr Bueno, a researcher on misinformation who's spent a decade looking at the anti-vaccination movement, says the film gave rise to communities of people across several social media platforms primed to hunt for news events to back up their views.
"They believe the anti-vaccine rhetoric that they are seeing," she says, "and they are joining in out of genuine concern without necessarily knowing that they're being misled."