Booster Shots More Effective During Omicron Emergence Period

Booster doses seem effective for the severe acute respiratory syndrome coronavirus 2 omicron variant, according to research published in the Jan. 21 early-release issue of the U.S. Centers for Disease Control and Prevention Morbidity and Mortality Weekly Report.

Amelia G. Johnson, Dr.P.H., from the CDC COVID-19 Emergency Response Team, and colleagues estimated incidence rate ratios (IRRs) among unvaccinated and fully vaccinated adults by receipt of booster dose during the pre-delta (April to May 2021), delta emergence (June 2021), delta predominance (July to November 2021), and omicron emergence (December 2021) periods. The researchers found that for unvaccinated versus fully vaccinated persons, the average weekly, age-standardized case IRRs decreased from 13.9 pre-delta to 8.7 as delta emerged and to 5.1 during delta predominance. Case IRRs decreased to 4.9 and 2.8 for fully vaccinated persons with booster doses and those without booster doses, respectively, during omicron emergence relative to October to November 2021.

Mark G. Thompson, Ph.D., from the CDC COVID-19 Response Team, and colleagues analyzed 222,772 encounters from 383 emergency departments and urgent care clinics and 87,904 hospitalizations from 259 hospitals among adults aged 18 years and older from Aug. 26, 2021, to Jan. 5, 2022, to examine real-world BNT162b2 vaccine effectiveness (VE). The researchers found that VE against laboratory-confirmed COVID-19-associated emergency department and urgent care encounters was 86, 76, and 94 percent 14 to 179 days after dose 2, ≥180 days after dose 2, and ≥14 days after dose 3, respectively, during the period of delta predominance. For the same intervals, the corresponding VE estimates were 52, 38, and 82 percent during omicron variant predominance.

"All adults who have received mRNA vaccines during their primary COVID-19 vaccination series should receive a third dose when eligible, and eligible persons should stay up to date with COVID-19 vaccinations," Thompson and colleagues write.