WASHINGTON (AP) — In March, as claims about the dangers and ineffectiveness of coronavirus vaccines spun across social media and undermined attempts to stop the spread of the virus, some Facebook employees thought they had found a way to help.

By altering how posts about vaccines are ranked in people's newsfeeds, researchers at the company realized they could curtail the misleading information individuals saw about COVID-19 vaccines and offer users posts from legitimate sources like the World Health Organization.

"Given these results, I'm assuming we're hoping to launch ASAP," one Facebook emp...