Comparing Absolute and Relative Vaccine Effectiveness of Primary and Booster COVID-19 Vaccines

When determining the coronavirus disease 2019 (COVID-19) vaccine effectiveness, evidence found the absolute vaccine effectiveness (aVE) to be a better metric than relative vaccine effectiveness (rVE). The findings of the study are published in the Open Forum Infectious Diseases.

“We found COVID vaccine primary series plus booster continues to provide substantial protection against COVID-19 hospitalization,” the researchers said. “However, we found that interpretation of the actual benefits of COVID-19 vaccine booster doses is difficult when considering rVE alone without the benefit of additional contextual data including aVE of the vaccine regimens being compared.”

The researchers included a total of 2060 patients hospitalized at 21 medical centers in the United States during between December 2021 and April 2022. All the patients, 1,104 COVID-19 cases and 956 controls, were immunocompetent and eligible for the COVID-19 booster.

The researchers found that the “relative vaccine effectiveness against COVID-19 hospitalization in boosted mRNA vaccine recipients versus primary series only was 66% (95% CI, 55%–74%); aVE was 81% (95% CI, 75%–86%) for boosted versus 46% (95% CI, 30%–58%) for primary.” Additionally, for boosted Janssen vaccine recipients versus primary series, rVE was 49% (95% CI, −9% to 76%); aVE was 62% (95% CI, 33%–79%) for boosted versus 36% (95% CI, −4% to 60%) for primary.

The researchers agree that the vaccine booster provides increased protection against COVID-19 hospitalization compared with a primary series. However, aVE is found to be a more useful metric than rVE, since rVE measures can lead to flawed interpretations of the added value of a new vaccination regimen.

—Priyam Vora

Reference:
Lewis N, Murray N, Adams K et al. Absolute and relative vaccine effectiveness of primary and booster series of COVID-19 vaccines (mRNA and adenovirus vector) against COVID-19 hospitalizations in the United States, December 2021–April 2022. Open Forum Infectious Diseases. 2023; 10(1). DOI: https://doi.org/10.1093/ofid/ofac698