The data released this week that helped convince the Food and Drug Administration to recommend a booster shot for Pfizer-BioNTech vaccine recipients also confirmed the extraordinary effectiveness of the initial two-dose regimen at preventing hospitalization and death.

The study, published in The Lancet medical journal, found the vaccine’s effectiveness at preventing COVID-19 dropped to 47 percent from 88 percent six months after the second dose. Yet the effectiveness at preventing hospitalization and death remained at 90 percent for at least six months, even against the highly transmissible Delta variant.

The study used research from Pfizer and an analysis of more than 3.4 members of the Kaiser Permanente Southern California health system between December 2020 and August 2021. The results, released in August, completed a peer review this week.

“Anyone over the age of 65 should consider getting a booster as long as it has been at least six months since they completed the first series of the vaccine,” says Eric Arlia, Hartford HealthCare’s Senior Director of Pharmacy. “Everything is specifically related to the Pfizer vaccine. There are no recommendations or approvals or guidance on switching from one brand of vaccine to another.”

The FDA granted the Pfizer-BioNTech vaccine full authorization in August — it had been available previously under emergency use authorization — and in September approved booster shots for people age 65 and older and others at high risk of severe illness.

“Still take precautions” after getting a booster, says Dr. Ulysses Wu, Hartford HealthCare’s System Director of Infection Disease and Chief Epidemiologist. “It’s not a silver bullet of protection. And even if it does protect people, you can still possibly become symptomatic and give it to somebody else.”

Johnson & Johnson said Tuesday it has asked the FDA to authorize booster shots for its single-dose COVID-19 vaccine, though it acknowledged the FDA and Centers for Disease Control and Prevention would determine who would get the boosters and when.

The FDA’s Vaccine and Related Biological Products Advisory Committee will consider booster requests from J&J and Moderna during a scheduled meeting Oct. 14-15.