Seroprevalence of infection-induced SARS-CoV-2 antibodies – United States, September 2021 to February 2022.

On April 26, 2022, this report was published online as MMWR early release.

In December 2021, the B.1.1.529 (Omicron) variant of SARS-CoV-2, the virus that causes COVID-19, became prevalent in the United States. Subsequently, the national COVID-19 infection rates peaked at their highest recorded levels. Therefore, the proportion of the population with SARS-CoV-2 antibodies (i.e. seroprevalence) could improve understanding of the incidence of COVID-19 at the population level. This report uses data from the CDC National Commercial Laboratory seroprevalence study and the 2018 American Community Survey to examine US trends in SARS-CoV-2 seroprevalence from September 2021 to February 2022. , According to age group.

The National Commercial Laboratory Serological Prevalence Study is a nationwide, cross-sectional repeat survey that estimates the proportion of populations in 50 US states, the District of Columbia, and Puerto Rico who have infection-causing antibodies to SARS-CoV-2. Sera are tested for nucleocapsid antibodies (anti-N), which are produced in response to infection but not in response to COVID-19 vaccines currently authorized for emergency use or approved by the United States Food and Drug Administration.§

During the period from September 2021 to February 2022, a convenient sample of blood samples submitted for clinical testing every 4 weeks was analyzed for anti-N antibodies. In February 2022, the sampling period was less than 2 weeks in 18 of 52 jurisdictions, and samples were not available from Two jurisdictions. Specimens for which the physician requested SARS-CoV-2 antibody testing were excluded to reduce selection bias. During the period from September 2021 to January 2022, the average sample size per 4 weeks was 73,869 (range = 64,969 – 81,468); The sample size for February 2022 was 45,810. Estimates of seroprevalence were assessed by 4-week periods overall and by age group (0-11, 12-17, 18-49, 50-64, and 65 years). To produce estimates, investigators distributed jurisdiction-wide results to the population using hijacking across the dimensions of age, gender, and urban status from 2018 American Community Survey data. (1). CIs were calculated using bootstrap resampling (2); Statistical differences were evaluated using non-overlapping CIs. All samples were tested by Roche Elecsys Anti-SARS-CoV-2 Immunoglobulin Assay. ** All statistical analyzes were performed using the R statistical software (version 4.0.3; R Foundation). This activity was reviewed by the CDC, approved by the respective institutional review boards, and was conducted in accordance with applicable federal law and CDC policy.††

During September-December 2021, the overall seroprevalence increased by 0.9-1.9 percentage points per 4 weeks. During December 2021 to February 2022, the overall US seroprevalence increased from 33.5% (95% CI = 33.1–34.0) to 57.7% (95% CI = 57.1–58.3). During the same period, the seroprevalence increased from 44.2% (95% CI = 42.8–45.8) to 75.2% (95% CI = 73.6–76.8) among children aged 0–11 years and from 45.6% (95% CI = 44.4). -46.9)) to 74.2% (95% CI = 72.8-75.5) among subjects aged 12-17 years (Fig. The seroprevalence increased from 36.5% (95% CI = 35.7–37.4) to 63.7% (95% CI = 62.5–64.8) among adults aged 18–49 years, 28.8% (95% CI = 27.9–29.8) to 49.8% (95% CI = 48.5–51.3) among those aged 50–64 years, and from 19.1% (95% CI = 18.4–19.8) to 33.2% (95% CI = 32.2–34.3) among those who They are between -65 years old.

The results presented in this report are subject to at least four limitations. First, adequate sampling may limit generalizability. Second, the lack of race and ethnicity data prevented weighting of these variables. Third, all samples were obtained for clinical testing and may be over-represented of people who have greater access to health care or who often seek care. Finally, these results may underestimate the cumulative number of SARS-CoV-2 infection because post-vaccination infection may lower anti-N titers,§§And the¶¶ Nor can anti-N seroprevalence explain the re-infection.

As of February 2022, approximately 75% of children and adolescents had serological evidence of previous SARS-CoV-2 infection, with nearly a third of them becoming newborns since December 2021. The largest increases in seroprevalence occurred during September 2021–February 2022, in the age groups least covered by vaccination; The proportion of the U.S. population fully vaccinated by April 2022 increased with age (5-11, 28%; 12-17, 59%; 18-49, 69%; 50-64, 80%; 65-years old, 90% ). *** Lower seroprevalence among adults over 65 years of age, who are at greater risk of severe disease from COVID-19, may also be associated with increased use of additional precautions with age (3).

These results demonstrate the high incidence of the Omicron variant, especially among children. The N antibody seropositivity should not be interpreted as protection against future infection. Vaccination remains the safest strategy for preventing complications from SARS-CoV-2 infection, including hospitalization in children and adults (4And the5). The post-infection COVID-19 vaccine provides additional protection against severe illness and hospitalization (6). stay informed††† With vaccination recommended for all eligible persons, including those with previous SARS-CoV-2 infection.

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