Third Dose of COVID-19 Vaccine Is Beneficial Among Older Medicare Beneficiaries

A third dose of the COVID-19 vaccine decreases the risk for COVID-19-related hospitalization and death among older adults up to 4 months, according to study findings published in The Journal of Infectious Diseases.

Researchers conducted a retrospective cohort study between December 2021 and March 2022 to evaluate the additional benefit provided by and the waning effectiveness of a third COVID-19 vaccine dose in the prevention of COVID-19-related outcomes. Community-dwelling Medicare Fee-for-Service beneficiaries aged 65 years and older who received 2 doses of Moderna or Pfizer-BioNTech vaccines between December 2020 and August 2021 were eligible for inclusion. The primary outcomes were COVID-19-related hospitalization, COVID-19-related mortality, and a composite outcome of COVID-19-related hospitalization and mortality. Marginal and structural Cox regression models were used to estimate the relative vaccine effectiveness of 2 vs 3 doses of COVID-19 vaccines.

A total of 8,135,020 patients were eligible for inclusion, of whom 1,193,696 (aged 70-74 years, 28.8%; women, 58.0%; White, 86.2%) comprised the Moderna 2-dose group, 1,093,015 (aged 70-74 years, 28.6%; women, 59.4%; White, 84.0%) the Pfizer BioNTech 2-dose group, 2,982,893 (aged 70-74 years, 30.1%; women, 57.4%; White, 88.0%) the Moderna 3-dose group, and 2,865,388 (aged 70-74 years, 29.9%; women, 58.5%; White, 86.8%) the Pfizer BioNTech 3-dose group.

Compared with 2 doses, a third dose of either Moderna (relative vaccine effectiveness, 77.2%; 95% CI, 76.0%-78.4%) or Pfizer-BioNTech (relative vaccine effectiveness, 72.5%; 95% CI, 70.8%-74.0%) vaccine provided substantial added benefit against COVID-19-related hospitalization at 14 to 60 days post-dose 3.

At 61 to 120 days after the third dose, the added benefit remained high; however, after more than 120 days post-dose 3, the added benefit was lower for both the Moderna (relative vaccine effectiveness, 42.1%; 95% CI, 37.5%-46.3%) and Pfizer-BioNTech (relative vaccine effectiveness, 51.0%; 95% CI, 48.0%-53.7%) vaccines.  

Among those with prior medically attended COVID-19 diagnoses, a third dose of Pfizer-BioNTech vaccine (relative vaccine effectiveness, 5.4%; 95% CI, -22.2% to 26.8%) no longer provided an added benefit after more than 120 days post-third dose, while a third dose of Moderna vaccine (relative vaccine effectiveness, 43.1%; 95% CI, 12.9%-62.8%) still provided some added benefit after more than 120 days post-third dose.

A third dose of Moderna vs Pfizer-BioNTech vaccine was more effective against COVID-19-related hospitalization at 14 to 60 (relative vaccine effectives, 35.2%; 95% CI, 30.2%-39.9%), 61 to 90 (relative vaccine effectives, 40.6%; 95% CI, 36.5%-44.6%), and 91 to 120 (relative vaccine effectives, 34.8%; 95% CI, 29.0%-40.2%) days post-third dose.

Study limitations include potential exposure misclassification, the inability to discriminate a third dose primary series authorized for immunocompromised individuals and a first booster authorized for the general population, lack of laboratory-confirmed diagnoses of COVID-19, and between-group differences in usage of COVID-19 treatments.

“These findings might help inform decisions regarding timing of seasonal COVID-19 vaccinations,” the researchers concluded.

This article originally appeared on Infectious Disease Advisor