Top 5 Takeaways

1. Vaccine Effectiveness: COVID-19 mRNA vaccines provided significant protection against hospitalization in adults with previous SARS-CoV-2 infection, with effectiveness higher after a booster dose.
2. Omicron vs. Delta: Vaccine effectiveness was lower during the Omicron-predominant period compared to the Delta-predominant period, but a booster dose significantly improved protection.
3. Booster Dose Benefits: A booster dose increased vaccine effectiveness to approximately 68% during the Omicron period and 58% during the Delta period.
4. Public Health Recommendation: All eligible individuals, including those with previous SARS-CoV-2 infection, should stay up to date with COVID-19 vaccinations to prevent hospitalization.
5. Study Design: The study used a test-negative design and data from the Cosmos EHR to compare vaccination status among hospitalized patients with previous SARS-CoV-2 infection.

Original Article Author and Citation

Corresponding Author

Ian D. Plumb, iplumb@cdc.gov

Suggested Citation

Plumb ID, Feldstein LR, Barkley E, et al. Effectiveness of COVID-19 mRNA Vaccination in Preventing COVID-19–Associated Hospitalization Among Adults with Previous SARS-CoV-2 Infection — United States, June 2021–February 2022. MMWR Morb Mortal Wkly Rep 2022;71:549-555. DOI: http://dx.doi.org/10.15585/mmwr.mm7115e2

Summary

The study evaluated the effectiveness of COVID-19 mRNA vaccines in preventing hospitalization among adults with a previous SARS-CoV-2 infection. Using data from the Cosmos EHR, the study found that vaccination, particularly with a booster dose, provided significant protection against hospitalization during both the Delta and Omicron periods. Vaccine effectiveness was highest after a booster dose, highlighting the importance of staying up to date with vaccinations.

Methods

The study used a test-negative design to estimate vaccine effectiveness (VE) against COVID-19–associated hospitalization among adults aged ≥18 years with a previous positive nucleic acid amplification test (NAAT) or COVID-19 diagnosis. Data were obtained from the Cosmos EHR, including over 135 million patients. Patients were categorized based on vaccination status and matched with control patients by age, state, and hospitalization period. VE was estimated using conditional logistic regression, adjusting for various factors such as sex, race/ethnicity, and underlying health conditions.

Discussion

The findings indicate that COVID-19 mRNA vaccines, especially with a booster dose, provide substantial protection against hospitalization in individuals with previous SARS-CoV-2 infection. The study highlights the reduced effectiveness of two doses during the Omicron period compared to the Delta period, but a booster dose significantly improved protection. The results support the recommendation for all eligible individuals to stay up to date with their COVID-19 vaccinations.

Conclusion

COVID-19 vaccination, particularly with a booster dose, is effective in preventing hospitalization among adults with previous SARS-CoV-2 infection. The highest level of protection is achieved with a booster dose, underscoring the importance of staying current with vaccinations to mitigate severe outcomes from COVID-19 reinfections.

This has been your booster shot of MMWR Info! Please check back for more MMWR, Public Health, and Programming Tutorial content daily.