Top 5 Takeaways

1. Vaccine Effectiveness Decline: The overall age-adjusted vaccine effectiveness (VE) against new COVID-19 cases declined from 91.8% to 75.0% during May 3–July 25, 2021.
2. Stable Hospitalization Protection: VE against hospitalization remained relatively stable, ranging from 89.5% to 95.1% during the same period.
3. Delta Variant Impact: The decline in VE against new cases coincided with the Delta variant’s increase from <2% to >80% in the U.S. region that includes New York.
4. Breakthrough Infections: Among fully vaccinated adults, 97.8% of new cases occurred ≥7 days after being fully vaccinated, with a median of 77 days.
5. Layered Prevention Approach: The findings support a layered approach to reduce new COVID-19 cases and hospitalizations, centered on vaccination and including other strategies like masking and physical distancing.

Original Article Author and Citation

Corresponding Author

Eli Rosenberg, eli.rosenberg@health.ny.gov

Suggested Citation

Rosenberg ES, Holtgrave DR, Dorabawila V, et al. New COVID-19 Cases and Hospitalizations Among Adults, by Vaccination Status — New York, May 3–July 25, 2021. MMWR Morb Mortal Wkly Rep 2021;70:1306–1311. DOI: http://dx.doi.org/10.15585/mmwr.mm7037a7

Summary

This study by the New York State Department of Health evaluated the effectiveness of COVID-19 vaccines in preventing new infections and hospitalizations among adults in New York from May 3 to July 25, 2021. The study found that while the vaccines remained highly effective against hospitalization, their effectiveness against new infections declined during the period, coinciding with the rise of the Delta variant and the relaxation of public health measures.

Methods

The study linked four statewide databases to create a cohort of adults aged ≥18 years in New York. It calculated the rates of new COVID-19 cases and hospitalizations among fully vaccinated and unvaccinated individuals, stratified by age group. Vaccine effectiveness was estimated weekly, and breakthrough infections were defined as new cases among fully vaccinated persons.

Discussion

The findings indicate that while COVID-19 vaccines are highly effective against hospitalization, their effectiveness against new infections has declined, likely due to the Delta variant and reduced public health measures. The study supports a multipronged approach to reduce COVID-19 cases and hospitalizations, emphasizing vaccination and additional preventive measures.

Conclusion

The study concludes that COVID-19 vaccines remain crucial in preventing severe illness and hospitalization. However, to further reduce new cases, a layered approach that includes vaccination, masking, and physical distancing is recommended.

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