A second booster shot of the Pfizer vaccine will provide additional short-term protection against the Omicron variant in older adults, but the shot's effectiveness will wane after just four weeks and nearly disappear entirely after eight, according to a new study out of Israel.
Protection against severe illness did not wane in the six-week period following the second booster, but the window was too short to determine whether a second booster provided more significant long-term protection against severe illness than just one booster.
The study centered on adults 60 and older. The findings, which were published in the New England Journal of Medicine this week, are consistent with previous evidence that vaccine effectiveness against infection disappears faster than against severe disease.
"For confirmed infection, a fourth dose appeared to provide only short-term protection and a modest absolute benefit," the study reads.
Israel has already authorized a fourth dose of the Pfizer vaccine — the two-shot vaccine and two boosters — for adults over 60 and other high-risk individuals.
The study results arrive as the U.S. Food and Drug Administration convenes a panel of outside advisers Wednesday to discuss how boosters will be utilized in the states moving forward. Last month, the agency authorized second booster doses of the Pfizer and Moderna vaccines for adults over 50, as well as the immunocompromised.
Though 66% of Americans are vaccinated, just 30% are boosted, suggesting they'll unlikely decide to get a second booster.