The percentage of Americans who have been infected with COVID-19 jumped from 34% in December 2021 to 58% in February 2022, a new study from the Centers for Disease Control and Prevention reveals.
This is the first time the seroprevalence of prior infection is more than 50% in the American population.
“I definitely expected that we were going to see an increase continue ... but I didn’t expect it to increase quite this much. But we follow the data ... and this is what the evidence is showing us,” lead study researcher Kristie E. N. Clarke, MD, said during a CDC media briefing April 26.
Researchers found that presence of antinucleocapsid (anti-N) antibodies from prior infection varied by age. The rate varied from as high as 75% in children and teenagers 17 years and younger to 33% in those 65 and older, for example.
The study showed that the anti-N antibodies were more common in age groups with the lowest vaccination numbers.
Combined with up-to-date CDC data on deaths, hospitalizations, and cases, the study provides a clearer picture of where we are now and where we might be headed in terms of the pandemic.
Vaccination still valuable
The fact that nearly 60% of Americans have antibodies from prior infection is not a reason to think people with a history of COVID-19 should skip vaccination, said CDC director Rochelle P. Walensky, MD.
“I can’t underscore enough that those with detectable antibodies from previous infection, we encourage them to still get vaccinated,” Dr. Walensky said.
“We do know that reinfections happen,” she said, “so that’s important in terms of thinking forward.”
The CDC continues to encourage all Americans to stay up to date with their COVID-19 vaccinations, said Dr. Clarke, colead for the CDC’s COVID-19 Epidemiology and Surveillance Taskforce Seroprevalence Team. “Having infection-induced antibodies does not necessarily mean you are protected against future infections.”
The study, published in the CDC’s Morbidity and Mortality Weekly Report (MMWR), did not evaluate antibody protection from COVID-19 vaccination.
It should also be noted that the study looked at presence or absence of anti-N antibodies, and not whether certain levels were linked to less or more protection.
Where are we now?
Dr. Walensky used the media briefing as an opportunity to share current COVID-19 numbers.
“Overall, we can continue to have some mixed trends. Deaths, fortunately, are continuing to trend downward with a 7-day average of about 300 per day, which represents an estimated 18% decline from the prior week,” she said.
Hospital admissions also remain low, at about 1,500 per day. “But we should note that for the second week in a row, they are slowly trending upwards,” Dr. Walensky said. There was an increase of about 9% at press time compared with the prior week.
Cases remain “comparatively low” to even where we were a month ago, at 44,000 per day,” Dr. Walensky said. “Although this too represents an increase of about 25% in the past week.”
Dr. Walensky noted that positive test numbers are not as reliable a metric as they were before the growth in use of rapid home tests. But it’s not the only measure. “We continue to believe that our PCR testing data, especially when we corroborate it with information from our other surveillance systems – like wastewater surveillance and emergency department surveillance – provide us a reliable picture of the trajectory of COVID-19 across our country.”
She recommended that people continue to consult the CDC’s COVID-19 county tracker to monitor local levels of COVID-19.
Dr. Walensky also shared recent findings from genomic sequencing that continue to show the predominance of the Omicron variant. “Essentially a hundred percent of what we’re finding now is Omicron,” she said. In terms of individual variants, the Omicron BA.1 variant is about 3% of circulating virus, the BA.2 variant is about 68%, and BA.2.12.1 makes up about 35%.
“We’re just starting to learn about the impact of BA2.121,” Dr. Walensky said. “It appears it might have a transmission advantage of about 25% over the BA2 subvariant.”
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