Though much remains uncertain, experts predicted many people will face new barriers to vaccination.

The Food and Drug Administration announced this week that it was likely to limit access to Covid vaccines among healthy children and adults this fall.

While the shots will most likely still be available for people 65 and older or with certain underlying conditions, F.D.A. officials say more research is needed to determine whether healthy Americans need a shot every year.

But critics say it is dangerous to limit access to vaccines for a virus that still leads to hospitalizations and deaths every day, and continues to evolve. Covid has been linked to more than 1.2 million deaths in the United States, though the rate of hospitalizations and deaths has fallen considerably.

The ongoing risk means that many people in the healthy category may still want a vaccine to avoid virus complications, or to protect a high-risk loved one or an infant who has never had Covid.

Here’s what experts expect if the plan goes forward.

Who will be eligible for the vaccine?

Historically, almost everyone has been eligible for Covid vaccines; the C.D.C. recommended the most recent vaccine for all Americans over 6 months of age.

But in an article published in The New England Journal of Medicine on Tuesday, F.D.A. officials said they would require new research into how effective the Covid vaccines are in healthy people before issuing an updated approval for a broader population. The vaccine is expected to remain available for anyone who is at least 65 or who has a medical condition that can increase the risk of severe illness or death.