Most of us have already had a case of COVID

From the Johns Hopkins daily health newsletter:

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US SEROPREVALENCE 

A study published April 26 in the US CDC’s Morbidity and Mortality Weekly Report (MMWR) estimates that 58% of the US population, including 75% of children, have been infected with SARS-CoV-2. Many of those infections occurred during the winter’s Omicron surge. The study reports on data from national commercial laboratories across all 50 states, Washington, DC, and Puerto Rico. Between September 2021 and February 2022, labs conducted convenience samples on blood specimens that were submitted for clinical testing in their labs, excluding samples that were testing for SARS-CoV-2 antibodies upon initial receipt. The median sample size for the group of labs was 73,869 each month, with a drop in the number of tests to 45,810 in February 2022, likely caused by disruptions from the surge in domestic infections fueled by the Omicron variant. The research team weighted samples by demographic data to produce estimates of seroprevalence. 

The team saw a slight, but steady, increase in seroprevalence between September and December 2021, increasing between 0.9-1.9% every 4 weeks. At the end of this collection period, the seroprevalence across the US sample was estimated to be 33.5%. Between December 2021 and February 2022, at the height of the Omicron surge, the team observed a spike in national seroprevalence, rising from 33.5% to 57.7%. Notably, during this period, children aged 0-11 saw an increase from 44.2% to 75.2% and those aged 12-17 saw a similar increase from 45.6% to 74.2%. Adult populations saw spikes in seroprevalence from 36.5% to 63.7% for individuals aged 18-49, 28.8% to 49.8% for those 50-64, and 19.1% to 33.2% among those aged 65 and older. The researchers noted several limitations in their study design, including restrictions of applicability tied to convenience sampling; limited race and ethnicity data; the potential for sampling bias due to the setting of sample collection; and the possibility that infection following vaccination resulted in reduced antibody titers.  

SARS-CoV-2 testing is only able to catch a fraction of cases occurring in the country, so serosurveys present an opportunity to better understand the scale of infections. Still, the study may not represent a full picture of COVID-19 in the country, nor does it indicate whether or not individuals with SARS-CoV-2 antibodies have persistent immunity to new infections. CDC Director Dr. Rochelle Walensky noted the study’s results and vaccine uptake show an increased level of community protection from SARS-CoV-2. She added that vaccination remains key in creating a more resilient population, urging those who remain unvaccinated, including those previously infected, to get vaccinated. 

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