lmost 60% of the U.S. population—and 75% of U.S. children—have evidence in their blood suggesting a past infection with the virus that causes COVID-19, according to new research from scientists at the U.S. Centers for Disease Control and Prevention (CDC) that looks at data from September 2021 to February 2022.
By that estimate, most people in the U.S.—almost 200 million—have had COVID-19 as of February. This is far more than the 80.8 millions cases that the CDC officially tallied as of April 26.
“We know that the reported cases are just the tip of the iceberg,” said Dr. Kristie Clarke, co-lead for the CDC’s COVID-19 Epidemiology and Surveillance Taskforce Seroprevalence Team, during a press briefing on April 26. Cases can go undetected if people don’t develop symptoms, don’t get tested, or use at-home rapid tests that aren’t reported to public-health officials. Clarke said that CDC research suggests there could have been three cases for each case reported in the Omicron wave. This would suggest millions of people were not aware of the contagious variant.
In the CDC’s new study, researchers used data on antibodies—proteins the body generates to fight off an infection—to better understand how many people in the U.S. previously had COVID-19. SARS-CoV-2, the virus responsible for COVID-19, is treated with antibodies. These antibodies are not produced by vaccines. This allows you to test your body for antibodies that can detect if someone may have been previously infected.
In the weeks that began in September, scientists analyzed blood samples taken from thousands of people throughout the U.S. for clinical testing. (The report didn’t specify why most people’s tests were submitted for testing, though it notes that people whose doctors specifically ordered SARS-CoV-2 antibody testing were excluded to avoid skewing the data.) Using those findings, the CDC estimated how much of the total U.S. population had antibodies—and thus had a prior COVID-19 infection—at each point in time.
The antibody prevalence jumped during the U.S.’s winter Omicron flood, which reached its peak in January at nearly a million cases each day.
According to the CDC, 34% of U.S. citizens had COVID-19 antibodies as of December 2021. After Omicron had decimated large swathes of U.S. citizens, 58% had antibodies suggesting a previous infection by February 2022. Roughly 75% of kids 17 and younger, who are less likely to be vaccinated than adults, had SARS-CoV-2 antibodies by February, according to the CDC’s research.
“While those who are under the age of 5 are not yet eligible for vaccination, the best way to protect them is to make sure that they are surrounded by people who are taking preventive measures like staying up to date with their vaccines,” Clarke said.
The antibody prevalence estimates in the report aren’t perfect, the CDC researchers say. All blood samples that were analyzed were submitted to clinical testing. Therefore, people with access and reason for seeking care may be overrepresented in this study. It’s also impossible to tell from this method whether someone has been infected multiple times. Researchers note that these estimates may be higher than necessary.
Although antibodies that are created to combat an infection may provide some protection in the future, the CDC warns they cannot replace vaccination. Infection-derived immunity is similar to the COVID-19 vaccines’ immunity, which may diminish over time.
“Vaccination remains the safest strategy for preventing complications from SARS-CoV-2 infection, including hospitalization among children and adults,” the agency’s researchers write in their report.
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