Department of Research & Evaluation News

A Kaiser Permanente study shows the Pfizer-BioNTech BNT162b2 BA.4/5 bivalent mRNA vaccine helped protect against a range of COVID symptoms and was effective against the COVID XBB strain sublineages. The most substantial benefit of the bivalent vaccine booster was keeping people out of the hospital and keeping people from becoming critically ill. The study was published in October 2023 in Lancet Respiratory Medicine.

“By the end of 2022, people who had been previously vaccinated with the original monovalent vaccines had little protection against COVID-19—even for hospital admission. The Pfizer bivalent vaccine restored that protection,” said Sara Tartof, PhD, the lead author of the study and an epidemiologist with the Kaiser Permanente Southern California Department of Research & Evaluation. “Few published studies have looked at the Pfizer bivalent vaccine across several clinical outcomes in a large population or  evaluated it against XBB.”

The monovalent vaccine contains an mRNA component from only one strain of virus, while the  bivalent vaccine, which was granted emergency use authorization on August 31, 2022, contains mRNA components from 2 strains of virus. The Pfizer bivalent was also authorized as a booster for children 12 to 17 years of age on the same date. The FDA granted the emergency use authorization at a time when the emerging data showed substantial waning of effectiveness of the monovalent vaccine against the newly emerged BA.4/5 omicron sublineage—even against severe outcomes like hospitalization—after only 3 to 6 months.

For this study, researchers analyzed the electronic health records from August 31, 2022, through April 15, 2023, for people diagnosed with acute respiratory infection and who had a COVID test within Kaiser Permanente Southern California.

Analyses were conducted for 123 419 encounters (24 246 COVID-19 cases and 99 173 test-negative controls), including 4,131 episode of critical illness (a subset of hospital admissions)  14,529 hospital admissions,  63,566 emergency department visits or urgent care visits, and  45,324 outpatient visits.

• For those with the bivalent booster compared with those who received at least 2 of the original monovalent boosters, the vaccine effectiveness was
  • 50% more against critical illness,
  • 39% more against hospital admission
  • 35% more against emergency department or urgent care visits, and
  • 28 % more against outpatient visits.
• The highest levels of protection were seen against hospital admission and critical illness.
• Waning of the bivalent booster from 0–3 months to 4–7 months after vaccination was evident for outpatient outcomes but was not evident for critical illness, hospital admission, and emergency department or urgent care outcomes.

In addition to Dr. Tartof, authors include Jeff M. Slezak, MS, Vennis Hong, MPH, Fagen Xie, PhD, Harpreet Takhar, MPH, Oluwaseye A Ogun, MD, Sarah Simmons, MPH, of the Kaiser Permanente Southern California Department of Research & Evaluation; Laura Puzniak, PhD, Joann M. Zamparo, MPH, Srinivas R. Valluri, PhD, Luis Jodar, PhD, and (senior author) John M. McLaughlin, PhD of Pfizer Inc., Collegeville, Pa; Timothy B. Frankland, MA, Kaiser Permanente Hawaii Center for Integrated Health Care Research; and Bradley K. Ackerson, MD, Southern California Permanente Medical Group, Harbor City. The senior author, Dr. Tartof, is also affiliated with the Kaiser Permanente Bernard J. Tyson School of Medicine in Pasadena, Calif.