Novavax had expected full approval for broader use by April 1, after the FDA reviewed data from a 30,000-person clinical trial showing the vaccine was safe and effective. But instead of a broad approval, the FDA asked the company to conduct more research.

The Food and Drug Administration says it has decided to continue approving COVID-19 vaccine updates for seniors and others at higher risk of severe disease, but will require vaccine makers to conduct major new clinical trials before approving them for wider use.

The FDA plans to require new clinical trials for approval of annual COVID-19 boosters for healthy Americans under 65.

US Food and Drug Administration officials are changing the agency's standards for updated COVID-19 booster shots with focus on seniors, high-risk persons.

WASHINGTON — Robert F. Kennedy Jr. clinched the political support needed to become the nation’s top health official by pledging to work within the decades-old federal system for approval and use of vaccines. Yet his regulators are promising big changes that cloud the outlook for what shots might even be available.

In a major policy shift, federal health officials anticipate the shots will be made available to adults 65 and older as well as children and younger adults who have one or more risk factors that make them more vulnerable to severe COVID-19.