Top 5 Takeaways

1. Higher Odds of COVID-19 in Previously Infected: Unvaccinated adults with previous SARS-CoV-2 infection had 5.49 times higher odds of laboratory-confirmed COVID-19 compared to fully vaccinated individuals without prior infection.
2. Vaccine-Induced Immunity More Protective: Among hospitalized adults, mRNA vaccine-induced immunity provided stronger protection against COVID-19 than infection-induced immunity.
3. Importance of Vaccination: The findings underscore the importance of COVID-19 vaccination for all eligible individuals, including those previously infected with SARS-CoV-2.
4. Secondary Analyses Consistent: Secondary analyses adjusting for different time intervals since infection or vaccination and during Delta variant predominance produced similar results to the primary analysis.
5. Moderna vs. Pfizer-BioNTech: The protective effect of vaccination appeared higher for Moderna vaccine recipients compared to Pfizer-BioNTech recipients.

Original Article Author and Citation

Corresponding Author

Catherine H. Bozio, ise7@cdc.gov

Suggested Citation

Bozio CH, Grannis SJ, Naleway AL, et al. Laboratory-Confirmed COVID-19 Among Adults Hospitalized with COVID-19–Like Illness with Infection-Induced or mRNA Vaccine-Induced SARS-CoV-2 Immunity — Nine States, January–September 2021. MMWR Morb Mortal Wkly Rep 2021;70:1539–1544. DOI: http://dx.doi.org/10.15585/mmwr.mm7044e1

Summary

This study examined hospitalizations for COVID-19–like illness among adults in nine states from January to September 2021. It compared the odds of laboratory-confirmed COVID-19 between unvaccinated individuals with previous SARS-CoV-2 infection and those fully vaccinated with an mRNA COVID-19 vaccine. The results showed that vaccine-induced immunity was more protective than infection-induced immunity.

Methods

Data were collected from 187 hospitals across nine states as part of the VISION Network. The study included adults aged ≥18 years hospitalized with COVID-19–like illness who had been tested for SARS-CoV-2 at least twice. Two groups were compared: unvaccinated individuals with previous SARS-CoV-2 infection and fully vaccinated individuals with no prior infection. Multivariable logistic regression was used to calculate adjusted odds ratios (aORs), accounting for various sociodemographic and health characteristics.

Discussion

The study found that unvaccinated individuals with previous SARS-CoV-2 infection had significantly higher odds of laboratory-confirmed COVID-19 compared to fully vaccinated individuals. This suggests that mRNA vaccine-induced immunity provides stronger protection. The findings were consistent across secondary analyses and during the Delta variant predominance. The study also noted higher protection for Moderna vaccine recipients and older adults.

Conclusion

The results highlight the importance of COVID-19 vaccination for all eligible individuals, including those previously infected with SARS-CoV-2. Vaccination provides stronger protection against COVID-19 than previous infection alone.

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