Top 5 Takeaways

1. Vaccine Effectiveness: Moderna’s vaccine was 86% effective and Pfizer-BioNTech’s was 75% effective in preventing COVID-19–associated hospitalizations ≥120 days after the second dose.
2. Antibody Levels: Antibody responses to both vaccines decreased over time, but Moderna recipients had higher antibody levels than Pfizer-BioNTech recipients.
3. Booster Importance: The findings suggest the importance of booster doses to maintain long-term protection against severe COVID-19, especially in older adults with underlying conditions.
4. Study Population: The study included 1,896 U.S. veterans hospitalized at five Veterans Affairs Medical Centers, with a high prevalence of underlying conditions.
5. Antibody Decline: Antibody levels among recipients of both vaccines declined significantly between 14–119 days and ≥120 days after the second dose.

Original Article Author and Citation

Corresponding Author

Kristina L. Bajema, kbajema@cdc.gov

Suggested Citation

Bajema KL, Dahl RM, Evener SL, et al. Comparative Effectiveness and Antibody Responses to Moderna and Pfizer-BioNTech COVID-19 Vaccines among Hospitalized Veterans — Five Veterans Affairs Medical Centers, United States, February 1–September 30, 2021. MMWR Morb Mortal Wkly Rep 2021;70:1700–1705. DOI: http://dx.doi.org/10.15585/mmwr.mm7049a2

Summary

This study assessed the comparative effectiveness of Moderna and Pfizer-BioNTech COVID-19 vaccines in preventing COVID-19–associated hospitalizations among U.S. veterans. It found that the Moderna vaccine was 86% effective and the Pfizer-BioNTech vaccine was 75% effective ≥120 days after the second dose. Antibody levels for both vaccines decreased over time, with Moderna recipients maintaining higher levels than Pfizer-BioNTech recipients. These results highlight the importance of booster doses to sustain long-term protection, particularly in older adults with underlying health conditions.

Methods

The study was conducted at five Veterans Affairs Medical Centers from February 1 to September 30, 2021. It included 1,896 hospitalized veterans with COVID-19–like illness. Vaccine effectiveness was measured by comparing the odds of full vaccination between case-patients (COVID-19 positive) and controls (COVID-19 negative). Antibody levels were assessed using residual clinical serum specimens from fully vaccinated controls, measuring IgG levels against SARS-CoV-2 antigens.

Discussion

The study found that both mRNA vaccines remained effective in preventing hospitalizations due to COVID-19, although antibody levels declined over time. Moderna recipients had consistently higher antibody levels compared to Pfizer-BioNTech recipients. The findings suggest that booster doses are crucial for maintaining long-term protection, especially in older adults with high prevalences of underlying conditions. The study also noted that antibody levels in this older, hospitalized cohort were lower than those in younger, healthier populations.

Conclusion

The study concludes that both Moderna and Pfizer-BioNTech vaccines are effective in preventing severe COVID-19, but antibody levels decline over time, necessitating booster doses. Continued monitoring of vaccine effectiveness and antibody levels is essential to understand the duration of protection and the need for booster doses.

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