Protection against hospitalization after a booster dose of Pfizer's COVID-19 vaccine wanes after three months, according to a study led by researchers at Oakland, Calif.-based Kaiser Permanente.
The findings, published April 22 in The Lancet Respiratory Medicine, showed a booster dose was about 80 percent to 90 percent effective at preventing hospital admissions and emergency department visits caused by delta and omicron within three months of receiving the shot. After three months, protection against hospitalization caused by omicron fell to about 55 percent, while protection against ED visits that did not result in hospitalization fell to 53 percent.
The study used Kaiser Permanente patient records from December 2021 through Feb. 6, 2022. Researchers analyzed 11,123 hospital admissions and ED visits that did not result in admission for acute respiratory infection.
"Pfizer BioNTech COVID-19 booster doses significantly improve protection against omicron, although that protection seems to wane after three months against emergency room visits, and even for hospitalization," said Sara Tartof, PhD, lead study author and epidemiologist at the health system's department of research and evaluation in Southern California. "Trends in waning against delta-related outcomes were generally similar to omicron but with higher effectiveness at each time point than those seen for omicron."