After the surge in infections fueled by the Omicron variant, more than half of blood samples collected in the United States tested positive for antibodies against COVID-19, the Centers for Disease Control and Prevention reported Tuesday. File photo by Jim Ruymen/UPI | License Photo
Nearly 60% of blood samples collected from people in the United States showed evidence by the end of February of previous infection with the virus that causes COVID-19, data released Tuesday by the Centers for Disease Control and Prevention showed.
This is after a marked increase in infections nationally between the beginning of December and the end of February, fueled by the spread of the Omicron variant of the virus, the agency said.
From Sept. 1 through Dec. 1 last year, the proportion of blood samples that tested positive for the presence of antibodies, or proteins produced by the immune system to fight diseases, against the virus rose 1% to 2% every four weeks, the CDC reported.
However, from Dec. 1 through Feb. 28, the proportion of blood samples that tested positive for antibodies increased to 58% from just under 34%, it said.
«This is the first time that population seroprevalence is over 50%,» Dr. Kristie Clarke, co-lead for the CDC’s COVID-19 Epidemiology and Surveillance Task Force Seroprevalence Team, told reporters on a call Tuesday. «This is what the evidence is showing us.»
Although the presence of antibodies against a virus in blood suggests at least some degree of immunity against it, testing positive for them «should not be interpreted as protection from future infection,» the agency researchers wrote.
The study did not measure whether people with prior infections had high enough antibody levels to protect against reinfection and severe illness, CDC officials said on the call.
«[For] those who have detectable antibody from prior infection, we still continue to encourage them to get vaccinated,» CDC Director Dr. Rochelle Walensky said.
«We don’t know when that infection was [and] we don’t know whether that protection has waned,» she said.
Vaccination remains the safest strategy for preventing complications from infection, including hospitalization among children and adults and getting the shots after infection provides additional protection against severe disease and hospitalization, she said.
«We don’t know as much about [the] level of protection [from past infection] than we do about the protection we get from both vaccines and boosters,» Walensky said.
The COVID-19 vaccine from Pfizer-BioNTech has been cleared for use in children ages 5 to 11 years since February, but likely won’t be greenlighted for those age 5 years and younger until June, according to reports.
Among children age 11 years and younger, 75% of samples collected by the end of February were positive for the virus, suggesting previous infection, up from 44% in December, according to the CDC.
Those ages 12 to 17 years saw a similar increase, to 74% from 46% over the same period, the agency said.
By the end of February, 64% of blood samples collected from adults ages 18 to 49 years showed signs of previous infection, up from 37% in December, the data showed.
For adults ages 50 to 64 years, seroprevalence — or the number of samples that tested positive for previous infection — rose to 50% from 29% over the same period, agency researchers said.
Those age 65 years and older saw seroprevalence increase to 33% from 19%, they said.
The findings are based on an analysis of blood samples collected from nearly 450,000 people in the United States between September 2021 and February this year, according to the CDC.
The high prevalence of positive results reflects the rise of the more contagious Omicron variant of the virus and its rapid spread, agency officials said.
That more children may have been infected with Omicron is not surprising, given that the CDC warned of a rise in hospitalizations among those age 18 years and younger as the variant began to spread across the country.
The CDC continues to recommend that people wear face coverings on public transportation despite a recent U.S. district court ruling that struck down mask mandates, Walensky said.
Still, «we do believe that there’s a lot of protection in the community both from vaccination, as well as from boosting and from prior infection,» she said.