Blood drawn by a registered nurse for a coronavirus antibody test on June 16, 2020 in Washington, DC.
Vin McNamee | Getty Images
According to the Centers for Disease Control and Prevention, three out of every 5 people in the US now have antibodies from a previous Covid-19 infection, with the proportion even higher among children, highlighting just how widespread the virus was during the winter omicron surge. .
The proportion of people with natural antibodies to Covid increased significantly from about 34% of the population in December to about 58% in February during an unprecedented wave of infection caused by the highly contagious omicron variant. The CDC analysis did not take into account people who had antibodies from the vaccination.
CDC published data in its weekly Morbidity and Mortality Report on Tuesday.
The increase in the prevalence of antibodies was most pronounced among children, which indicates a high frequency of infection in children during the winter omicron wave. About 75% of children and teens now have antibodies from previous Covid infections, up from about 45% in December.
The high incidence among children is likely due to lower vaccination rates than in adults. Only 28% of children aged 5 to 11 and 59% of adolescents aged 12 to 17 were fully vaccinated as of April. Children under 5 years of age are not yet vaccinated.
About 33% of people aged 65 and over, the group with the highest vaccination rates, had antibodies from the infection. Approximately 64% of adults aged 18 to 49 and 50% of people aged 50 to 64 had antibodies.
The CDC analyzed about 74,000 blood samples every month from September to January from a national network of commercial laboratories. The sample size dropped to around 46,000 blood samples in February. The CDC tested the samples for a specific type of antibody that is produced in response to a Covid infection, not as a result of vaccination.
CDC officials told reporters on Tuesday that the study did not assess whether people with previous infections have high enough levels of antibodies to protect against reinfection and severe illness. However, CDC Director Dr. Rochelle Walensky said health officials believe there are many protections against vaccination, booster vaccination and infection in communities across the country, and warns that vaccination is the safest strategy to protect against virus.
“Those who have antibodies from a previous infection, we continue to encourage them to get vaccinated,” Walensky told reporters during a telephone conversation. “We don’t know when this infection was. We do not know if this protection has been weakened. We don’t know as much about this level of protection as we do about the protection we get from both vaccines and boosters.”
Scientists in Qatar, affiliated with Cornell University, found that natural infection provides about 73% protection from hospitalization if a person is re-infected with BA.2. However, three doses of the Pfizer vaccine provided a much higher protection against hospitalization at 98%. The study, published in March, has not been peer-reviewed.
About 66% of the US population is fully vaccinated, and 77% have received at least one dose, according to the CDC.
Infections and hospitalizations are down more than 90% from the peak of the omicron wave in January, when U.S. infections rose to an average of more than 800,000 a day. New cases are on the rise again due to sub-option BA.2. Another sub-option, BA.2.12.1, is currently gaining momentum in the US, accounting for about 29% of new infections, according to the CDC. Walensky said the public health agency believes BA.2.12.1 is spreading about 25% faster than BA.2. However, she said the CDC does not expect to see more severe illness from BA.2.12.1., although research is ongoing.
More than 98% of the US population lives in areas where they are not required to wear masks indoors as per CDC guidance due to low levels of Covid in the community, which accounts for both infections and hospitalizations. A U.S. District Judge last week overturned a CDC order to use masks on public transportation, although the Justice Department has filed an appeal. Walensky said the CDC continues to encourage people to wear masks on public transportation.