CDC: Updates in COVID-19, 58% seroprevalence in US

The CDC held a media briefing regarding COVID-19 updates that included current cases and new data from a report published in the Morbidity and Mortality Weekly Report on seroprevalence in the U.S.

As of April 25, overall COVID-19 deaths have decreased by 13.2% while confirmed COVID-19 hospital admissions and COVID-19 cases have both increased 6.6% and 22.7%, respectively, compared with the previous week. Data show more than 650,000 polymerase chain reaction tests are still performed daily, but there are 70-fold fewer cases, reflecting a reliable drop in overall cases.

“We’re sequencing thousands of viruses per week through a national SARS-CoV-2 strain surveillance in contracts with diagnostic and sequencing groups across the country to understand what is out there in the United States,” CDC Director Rochelle P. Walensky, MD, MPH, said during the media briefing. “Essentially 100% of what we’re finding now is omicron, though different lineages or sub-lineages may be more common in each region. This means that if a new variant were starting to spread, we would identify it quickly.”

In addition, researchers have found the BA.2.12.1 variant makes up almost 30% of all nationally identified sequences. BA.2.12.1 appears to have a transmission advantage of 25% over the other BA.2 subvariants, but studies are underway to understand its impact on vaccine effectiveness.

Kristie E.N. Clarke, MD, MSCR, FAAP, co-lead for the CDC COVID-19 Emergency Response Team, and colleagues examined trends in infection-induced SARS-CoV-2 seroprevalence in the U.S. from September 2021 to February 2022 by age group using data from the CDC’s National Commercial Laboratory Seroprevalence study. Researchers analyzed a sample of blood specimens every 4 weeks for anti-nucleocapsid antibodies, which are produced in response to infection but not in response to currently authorized vaccines.

The median sample size per 4-week period was 73,869 from September 2021 to January 2022 and 45,810 during February 2022.

Overall, U.S. SARS-CoV-2 seroprevalence increased by 0.9 to 1.9 percentage points per 4-week period from September to December 2021 and increased from 33.5% to 57.7% from December 2021 to February 2022.

Children aged 0 to 11 years (from 44.2% to 75.2%) and children aged 12 to 17 years (from 45.6% to 74.2%) demonstrated the highest SARS-CoV-2 seroprevalence from December 2021 to February 2022. In contrast, individuals aged 65 years and older demonstrated the lowest seroprevalence from December 2021 to February 2022 (from 19.1% to 33.2%). Seroprevalence among adults aged 18 to 49 years (from 36.5% to 63.7%) and adults aged 50 to 64 years (from 28.8% to 49.8%) showed similar increases during the same period.

Regarding limitations, Clarke noted that this methodology cannot detect reinfections, and emerging data suggest infection after vaccination may be less likely to lead to detectable antibodies.

“We want to keep all people in our country as healthy and safe as possible,” Clarke said. “So, it is important for either adults or children who have been previously infected to get vaccinated, if eligible.”