Top 5 Takeaways

1. Omicron Surge: The Omicron variant led to the highest recorded national COVID-19 case rates in the U.S. during December 2021.
2. Seroprevalence Increase: Overall seroprevalence of SARS-CoV-2 antibodies in the U.S. increased significantly from 33.5% in December 2021 to 57.7% in February 2022.
3. Age Group Differences: Children aged 0–11 years and adolescents aged 12–17 years saw the highest increases in seroprevalence, reaching approximately 75% by February 2022.
4. Vaccination and Seroprevalence: Lower seroprevalence was observed among older adults (≥65 years) who had higher vaccination rates and possibly took more precautions.
5. Limitations: The study’s limitations include convenience sampling, lack of race and ethnicity data, potential overrepresentation of those with greater healthcare access, and underestimation of cumulative infections.

Original Article Author and Citation

Corresponding Author

Kristie E.N. Clarke, vhz9@cdc.gov

Suggested Citation

Clarke KE, Jones JM, Deng Y, et al. Seroprevalence of Infection-Induced SARS-CoV-2 Antibodies — United States, September 2021–February 2022. MMWR Morb Mortal Wkly Rep 2022;71:606-608. DOI: http://dx.doi.org/10.15585/mmwr.mm7117e3

Summary

This report examines the seroprevalence of infection-induced SARS-CoV-2 antibodies in the U.S. from September 2021 to February 2022. The study found a significant increase in seroprevalence, particularly among children and adolescents, coinciding with the spread of the Omicron variant. The findings highlight the importance of vaccination as a strategy for preventing severe COVID-19 complications.

Methods

The study utilized data from the CDC’s national commercial laboratory seroprevalence study and the 2018 American Community Survey. Blood specimens were tested for anti-nucleocapsid antibodies every 4 weeks, and results were weighted to population demographics. Statistical analyses were conducted using R software, and the study was approved by institutional review boards.

Discussion

The report discusses the rapid increase in seroprevalence during the Omicron surge, particularly among younger age groups with lower vaccination rates. It also addresses the limitations of the study, including potential biases and the inability to account for reinfections or lower antibody titers post-vaccination.

Conclusion

The findings underscore the high infection rate of the Omicron variant and the importance of vaccination for preventing severe disease. The study recommends staying up to date with COVID-19 vaccinations for all eligible individuals, including those previously infected with SARS-CoV-2.

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