Skip to main content
2024 ISPE Annual Meeting Main banner
Icon Legend
This session is not in your schedule.
This session is in your schedule. Click again to remove it.
Back
Evaluation

Oral Presentation

Session: Assessing COVID-19 Vaccine Effectiveness

Added Benefit and Waning Effectiveness of a Third-Dose mRNA COVID-19 Vaccine in Community-Dwelling Medicare Beneficiaries Aged ≥65 Years in Omicron Period

Tuesday, August 27, 2024
8:15 AM – 8:30 AM CEST
Location: Conv Hall I C
Background: U.S. older adults (people aged ≥65 years) were disproportionately impacted by the COVID-19 pandemic. It is important to evaluate real-world effectiveness of mRNA COVID-19 vaccines among this vulnerable population.

Objectives: We evaluated the added benefit of third doses versus second doses of mRNA COVID-19 vaccines and if effectiveness wanes over time among community-dwelling older adults during an Omicron-dominant period.

Methods: We conducted a real-world retrospective cohort study using Medicare Fee-for-Service claims data among U.S. community-dwelling beneficiaries aged ≥65 years. Beneficiaries were followed during high COVID-19 circulation periods from December 19, 2021-March 26, 2022. Time-varying exposures included second and third doses of Moderna or Pfizer-BioNTech COVID-19 vaccines. We used inverse probability of treatment weighting and Cox proportional hazard models to estimate relative vaccine effectiveness (RVE) against COVID-19-related outcomes (e.g., hospitalization and death) by vaccine dose and brand.

Results: 8,135,020 two-dose mRNA COVID-19 vaccinated community-dwelling beneficiaries were eligible for the study, of whom 73.3% received a third dose by March 26, 2022. Third doses provided substantial added benefit against COVID-19-related outcomes throughout the observed follow-up time. While the added benefit was greatest against COVID-19-related death, COVID-19-related hospitalization had higher outcome counts that allowed for more precise RVE estimates. Against COVID-19 hospitalization, the third-dose added benefit was consistent for 120 days since third-dose vaccination (e.g., RVE at 14-60 days was 77.2% [95% confidence interval (CI): 76.0%-78.4%] for Moderna and 72.5% [95% CI: 70.8%-74.0%] for Pfizer-BioNTech), and was still significant but substantially lower afterwards (RVE at >120 days was 42.1% [95% CI: 37.5%-46.3%] for Moderna and 51.0% [95% CI: 48.0%-53.7%] for Pfizer-BioNTech). For those with prior medically-attended COVID-19 diagnosis, the added benefit against COVID-19 hospitalization was statistically significant for both brands until 120 days, and remained significant for Moderna after 120 days. Moderna three-dose vaccines were more effective against COVID-19 hospitalization than Pfizer-BioNTech three-dose vaccines for 14-120 days, but after 120 days there was no evidence of a difference in effectiveness between brands in the overall population.

Conclusions: A third dose of an mRNA COVID-19 vaccine provided substantial added benefit against severe COVID-19-related outcomes in this vulnerable population—even among those with prior COVID-19. The added benefit of a third dose remained high for at least 4 months during high COVID-19 circulation periods.