SARS-CoV-2 seroprevalence in US was 83% before surge of delta infections
Based on testing of more than 1.4 million blood donations, researchers estimated that the SARS-CoV-2 seroprevalence from infection or vaccination among Americans aged 16 years or older was 83% in May, before the delta variant surge.
Jefferson M. Jones, MD, MPH, a medical officer at the CDC, and colleagues conducted a repeated cross-sectional study each month from July 2020 through May 2021 that tested specimens from 17 blood collection organizations with donations from all 50 states, Washington, D.C., and Puerto Rico.
After December, when the FDA authorized the first COVID-19 vaccines for use, they began testing specimens to differentiate whether seroprevalence was from infection or vaccination.
They included 1,443,519 blood donation samples in their analysis. Of these, 50.8% were from women, 12.1% were from people aged 16 to 29 years, and 20.2% were from people aged 65 years or older.
From July through December 2020, the estimated infection-induced seroprevalence among donors increased from 3.5% (95% CI, 3.2%-3.8%) to 11.5% (95% CI, 11.1%-11.8%), Jones and colleagues reported.
By May 2021, the combined seroprevalence among Americans had increased to 83.3% (95% CI, 82.9%-83.7%), and infection-induced seroprevalence increased to 20.2% (95% CI, 19.9%-20.6%), the researchers reported.
“Several large studies have shown that among individuals who are seropositive from prior SARS-CoV-2 infection, COVID-19 incidence is reduced by 80% to 95%, similar to vaccine efficacy estimates,” the authors wrote. “However, infection- and vaccination-induced protection might be reduced in the setting of SARS-CoV-2 variants, and infection-induced protection might wane more quickly than vaccine-induced protection.”
CDC. COVID-19 Data Tracker. National Blood Donor Seroprevalence Survey. https://covid.cdc.gov/covid-data-tracker/#nationwide-blood-donor-seroprevalence. Accessed September 8, 2021.