Seniors older than 65, adults with health problems, and adults in high-risk jobs or living situations should receive a Moderna COVID-19 booster six months after their initial vaccination, the Vaccines and Related Biological Products Advisory Committee said Thursday.

Its nonbinding vote goes to the U.S. Food and Drug Administration (FDA) next. If the FDA accepts the panel’s vote, it will send the emergency use authorization to the Centers for Disease Control and Prevention (CDC) for approval. The panel is scheduled to review a Johnson & Johnson booster on Friday.

How effective is the booster? A study with 344 participants found that antibody levels declined after six months but returned after a half-dose shot. Moderna said a half-dose was effective enough and would prevent side effects without draining the vaccine supply.

The study was too small to research rare heart inflammation, which has led some European countries to tell young men not to get Moderna’s vaccine. Some vaccine advisers said the data did not fully convince them that booster shots are necessary, but they cannot afford to lose healthcare workers to sickness amid a national worker shortage.

As of Wednesday, 66.2 percent of the eligible American population has been fully vaccinated for COVID-19, according to the CDC.

This story originally appeared in WORLD. © 2021, reprinted with permission. All rights reserved.