The Centers for Disease Control and Prevention (CDC) has estimated that almost 1 out of 4 people in the U.S. still hadn’t been exposed to COVID-19 by the end of 2022 after nearly three years of the pandemic.

In its final survey looking at the period between October and December 2022, the CDC estimated that about 77.5 percent of people had infection-induced antibodies against the SARS-CoV-2 virus.

The CDC began conducting studies looking into seroprevalence, the presence of antibodies against a virus in someone’s blood, beginning in January 2022. The agency observed seroprevalence in three-month increments over the course of last year.

Broken down by demographics, younger people — aged between 16 and 29 — had the highest percentage of natural antibodies at 87.1 percent, with this percentage decreasing among older groups.

Across racial groups, Hispanic individuals had the highest rate of naturally induced antibodies at 80.6 percent. Black, white and other racial/ethnic groups all shared about the same rate of natural antibodies, around 77 percent.

However, non-Hispanic Asians were found to have significantly lower rates of infection-induced antibodies than the others groups, with 66.1 percent found to have the antibodies. While the CDC did not provide an explanation for this, earlier data had found that Asians in the U.S. had generally lower infection rates.

An analysis released by KFF last year found that Asians had the lowest cumulative infection rate among racial/ethnic groups from 2020 to 2022.

While about 3 out of 4 people carried antibodies from natural infections, nearly all people — 96.7 percent — were found to have some form of COVID-19 antibodies in their systems due to vaccination, infection or a combination of both.

The data needed for the CDC’s study was collected by looking at blood from roughly 143,000 donors within a three-month period.

During the first quarter of 2022 about half of the U.S. had infection-induced antibodies in their blood. The CDC is not currently planning any more seroprevalence studies.

While vaccines also induce the immune system to create antibodies against a virus, a difference between the types of antibodies can be detected through antibody testing, which the CDC previously said could be done for “clinical and public health purposes.”

As researchers from Johns Hopkins University noted in a 2021 study, naturally infected individuals produce antibodies targeting several parts of a virus. The mRNA vaccines that have become widely used to protect against COVID-19 are designed to induce antibodies that look for only the spike proteins on the surface of the virus.

Antibodies are believed to last several months whether from infection or immunization, though some data suggests natural immunity wanes faster than immunity induced through vaccines.

Health officials are aiming to refresh nationwide immunity against COVID-19 this fall, with vaccine manufacturers preparing for a vaccine campaign targeting the XBB 1.5 omicron subvariant. Moderna has already requested authorization for its updated COVID shot.

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