The threat of Covid infections has not gone away, but the vaccines that help protect against them will be harder to come by this season.

Under President Trump and Health Secretary Robert F. Kennedy Jr., federal health officials have limited who qualifies for Covid shots. On Wednesday, the Food and Drug Administration approved updated versions only for people who are 65 or older and people who have a medical condition that puts them at higher risk.

The F.D.A. decision creates a fractured and confusing landscape. Healthy adults under 65 may have to jump through hoops to get a shot, if they are able to get one at all. The same is true for healthy children, the youngest of whom are at high risk of Covid complications simply by virtue of their age.

Here is where things stand, and what you can do.

When will the vaccines be available?

Representatives for Moderna and Pfizer said they would ship their updated vaccines almost immediately upon receiving F.D.A. approval. Those shots should begin to reach doctor’s offices and pharmacies after a few days.

Sanofi, which markets the Novavax shot, expects to make its vaccine available in “early fall,” a spokesman said.

Am I eligible for a vaccine?

It depends on your age and health. That’s a major change: Covid vaccines were previously approved for all Americans 6 months and older, but the F.D.A. is now limiting eligibility, a move opposed by many medical experts.