43% of Americans have had COVID-19, CDC says

More than 140 million Americans have had the coronavirus, according to estimates from blood tests that reveal antibodies from infection - about double the rate regularly cited by national case counts.

The estimates, compiled by the Centers for Disease Control and Prevention, show that about 43% of the country has been infected by the virus. The study shows that the majority of children have also been infected.

The data goes through late January, when the omicron variant of the coronavirus was causing more than 500,000 cases a day, meaning the number of Americans now infected is considerably higher. The data comes from 72,000 blood samples taken in January.

The highly infectious variant has caused case counts to skyrocket. As of late November, just before the omicron variant began spreading in the United States, the blood test study estimated that 103 million people had been infected. By that measure, 37 million new people caught the virus over two months ending in late January.

Every two weeks, the CDC gathers tens of thousands of blood tests analyzed by commercial labs nationwide for reasons unrelated to the coronavirus, such as checkups or other medical treatment. Those samples are also tested for coronavirus antibodies. The percentage of people with antibodies is known as seroprevalence.

The blood test study includes infections throughout the pandemic but counts each person only once. Daily coronavirus case rates tally every known infection, so many people who have had reinfections are counted again and again. The estimated 140 million is well over double the number of people included in counts by The Washington Post or government agencies as of late January.

The blood tests count only antibodies from natural infection, including asymptomatic cases, not from vaccination. The study measures the presence of antibodies. It does not indicate whether there is strong protection against subsequent infection.

Just under half of adults up to 49 have been infected, the CDC estimates. The rate drops to 37% for people 50 to 64 and 23% of people 65 or older.

The coronavirus is much deadlier for older people. Half of the people who have died of COVID-19 have been age 75 or older. Vaccination and other preventive measures have been concentrated on the most vulnerable older people. Younger people have much lower vaccination rates and are much more likely to be working in jobs or attending school, where they risk exposure.

At least half of the population in 14 states has been infected, blood tests showed, from 56% in Wisconsin to half in Georgia. The other states with a majority infection rate, in descending order, are Iowa, Illinois, Ohio, Wyoming, Texas, Indiana, Mississippi, Nebraska, Michigan, New Jersey, Tennessee and Louisiana. New York is just under that level, at 49%.

The lowest infection rate is in Vermont, with 18%. The next-lowest states in ascending order are Hawaii, Maine, Oregon, Washington, New Hampshire, Virginia and Massachusetts, which tops the lowest states with 37%.

Nevada was not included in the study, and there was insufficient data for North Dakota, Arizona and Utah.

Just before the omicron variant, a seroprevalence study that included both vaccination and natural infection found antibodies in more than 90% of adults, but that did not prevent omicron's enormous infection rates, hospitalization and death, said Kristen Nordlund, a CDC spokeswoman.

Vaccination or exposure to the coronavirus may have reduced the deadliness and severity of the omicron wave, Nordlund said.

Scientists still can't explain why some people get the virus and others do not. A CDC study of disease spread within households during the omicron wave found that 53% of people in a household with an infected person also caught the virus. Vaccination, mask-wearing and isolation within the household all reduced transmission and protected other members of the household. But even in households without isolation, vaccination or mask-wearing, not everyone caught it.

Another study of seroprevalence that examined a community after a coronavirus wave also found that it picked some people and skipped others, said William Powderly, head of the Institute for Public Health at Washington University of St. Louis.

The wave dissipated even though a vast majority of people tested showed no antibodies, Powderly said, so they were susceptible to the disease raging around them but didn't catch it.