Top 5 Takeaways

1. Vaccine Effectiveness: COVID-19 vaccines remained highly effective against hospitalization and death, even with the emergence of the Delta variant and waning immunity.
2. Impact of Booster Doses: Booster doses provided higher protection against infection and death, particularly during the Delta-predominant period and the emergence of the Omicron variant.
3. Age-Specific Benefits: The protective benefits of booster doses were especially significant for individuals aged 50–64 and ≥65 years.
4. Incidence Rate Ratios (IRRs): IRRs for unvaccinated versus fully vaccinated persons decreased over time, particularly with the emergence of the Omicron variant.
5. Public Health Recommendation: All eligible individuals should stay up to date with COVID-19 vaccinations, including booster doses, to maintain high levels of protection.

Original Article Author and Citation

Corresponding Author

Heather M. Scobie, vih8@cdc.gov

Suggested Citation

Johnson AG, Amin AB, Ali AR, et al. COVID-19 Incidence and Death Rates Among Unvaccinated and Fully Vaccinated Adults with and Without Booster Doses During Periods of Delta and Omicron Variant Emergence — 25 U.S. Jurisdictions, April 4–December 25, 2021. MMWR Morb Mortal Wkly Rep 2022;71:132–138. DOI: http://dx.doi.org/10.15585/mmwr.mm7104e2

Summary

This study evaluated the impact of full vaccination and booster doses on COVID-19 incidence and death rates among adults in 25 U.S. jurisdictions during the periods of Delta and Omicron variant emergence. The findings highlighted the sustained effectiveness of vaccines against severe outcomes and the additional benefits of booster doses, particularly for older adults.

Methods

Data on weekly COVID-19 cases and associated deaths by vaccination status were collected from 25 state and local health departments. The analysis included fully vaccinated persons with and without booster doses and excluded partially vaccinated individuals. Incidence rate ratios (IRRs) were calculated to compare rates between unvaccinated and vaccinated groups across different periods.

Discussion

The study found that COVID-19 vaccines significantly reduced the risk of infection and death, with booster doses providing additional protection. The emergence of the Omicron variant led to increased case rates among both vaccinated and unvaccinated individuals, but the relative protection offered by booster doses remained evident. The findings underscore the importance of staying up to date with COVID-19 vaccinations.

Conclusion

COVID-19 vaccines, including booster doses, are crucial in reducing the risk of infection and severe outcomes. Public health efforts should continue to focus on increasing vaccination coverage and encouraging booster doses to maintain high levels of protection, especially among older adults.

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