Top 5 Takeaways

1. High Vaccine Effectiveness: COVID-19 mRNA vaccines were 86.8% effective in preventing COVID-19–associated hospitalization among U.S. veterans.
2. Effectiveness Across Variants: The effectiveness remained high during both pre-Delta (84.1%) and Delta variant predominance (89.3%) periods.
3. Age-Related Differences: Vaccine effectiveness was lower among veterans aged ≥65 years (79.8%) compared to those aged 18–64 years (95.1%).
4. Diverse Population: The study included a racially diverse group of veterans, with 48.9% being non-Hispanic Black and 7.9% Hispanic.
5. Importance of Vaccination: The findings reinforce the importance of COVID-19 vaccination to prevent hospitalizations, especially among high-risk groups like veterans.

Original Article Author and Citation

Corresponding Author

Kristina Bajema, media@cdc.gov

Suggested Citation

Bajema KL, Dahl RM, Prill MM, et al. Effectiveness of COVID-19 mRNA Vaccines Against COVID-19–Associated Hospitalization — Five Veterans Affairs Medical Centers, United States, February 1–August 6, 2021. MMWR Morb Mortal Wkly Rep 2021;70:1294–1299. DOI: http://dx.doi.org/10.15585/mmwr.mm7037e3

Summary

This study assessed the effectiveness of COVID-19 mRNA vaccines (Pfizer-BioNTech and Moderna) in preventing COVID-19–associated hospitalizations among U.S. veterans. Conducted at five Veterans Affairs Medical Centers (VAMCs) from February 1 to August 6, 2021, the study found an overall vaccine effectiveness of 86.8%. The effectiveness was consistent across periods of pre-Delta and Delta variant predominance. The study highlighted the importance of vaccination, especially for older adults and those with underlying health conditions.

Methods

The study used a test-negative case-control design involving adults aged ≥18 years hospitalized at five VAMCs. Patients were included if they had COVID-19-like illness and a molecular test for SARS-CoV-2 within 14 days before or during the first 72 hours of hospitalization. Case-patients were those with positive SARS-CoV-2 tests, and controls had negative tests. Data were collected from electronic health records, and vaccine status was verified through state immunization registries where available. Full vaccination was defined as receiving both doses of an mRNA vaccine ≥14 days before the qualifying test. Vaccine effectiveness was estimated using multivariable logistic regression models.

Discussion

The study found that mRNA vaccines were highly effective in preventing COVID-19–associated hospitalizations among a diverse group of U.S. veterans, even during the Delta variant predominance. However, effectiveness was lower among older adults (≥65 years). The findings support the importance of vaccination, particularly for high-risk groups. The study’s limitations include its non-representative sample and potential confounding factors like unmeasured behaviors.

Conclusion

COVID-19 mRNA vaccines are highly effective in preventing hospitalizations among U.S. veterans, including during periods of Delta variant predominance. The findings underscore the need for vaccination, especially among older adults and those with underlying conditions. Further evaluations are needed to assess vaccine effectiveness across different age groups and over time.

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