The Coronavirus has infected more than half of Americans, the CDC reports

Sixty percent of Americans, including 75 percent of children, had been infected with the coronavirus by February, federal health officials reported Tuesday, another milestone in a pandemic that continues to confuse expectations.

The highly contagious variant of the Omicron was responsible for much of the toll. In December 2021, when the variant began to spread, only half of the people had antibodies indicating a previous infection. according to new research by the Centers for Disease Control and Prevention.

While the numbers came as a shock to many Americans, some scientists said they expected the figures to be even higher given the contagious variants that have marched across the nation over the past couple of years.

There may be good news in the data, some experts said. A population-wide immunity boost can offer at least a partial bulwark against future waves. And the trend could explain why the tide that’s now roaring through China and many European countries has been dampened in the United States.

A high percentage of previous infections can also mean that there are now fewer cases of life-threatening illnesses or deaths than infections. “We will see less and less severe disease and an ever greater shift towards clinically mild disease,” said Florian Krammer, an immunologist at the Mount Sinai Icahn School of Medicine in New York.

“It will be increasingly difficult for the virus to do serious damage,” he added.

Administration officials also believe the data hints at a new phase of the pandemic where infections can sometimes be common but cause less damage.

During a press conference on Tuesday, Dr. Ashish Jha, the White House’s new Covid coordinator, said stopping the infections “wasn’t even a political goal. The goal of our policy should be: of course, to minimize infections whenever possible, but to make sure that people do not get seriously ill. “

The average number of new confirmed cases per day in the United States – more than 49,000 as of Monday, according to a New York Times database – it is comparable to the levels last seen at the end of Julyalso as cases they increased by more than 50 percent Over the past two weeks, infectious disease experts have attributed a trend to the new sub-variants of Omicron.

Dr Jha and other officials warned against complacency and urged Americans to continue receiving vaccinations and booster vaccinations, stating that antibodies from previous infections did not guarantee protection from the virus.

According to the new research, during the Omicron wave, infections increased most sharply among children and adolescents. Previous infections have increased at least among adults aged 65 and over, who have the highest vaccination rates and may be more likely to take precautions.

“Evidence of previous Covid-19 infections has increased substantially in every age group,” said Dr. Kristie Clarke, the agency researcher who led the new study, said at a news conference Tuesday.

The widespread infection raises a troubling prospect: a potential increase in long Covid cases, a little-known constellation of persistent symptoms.

Up to 30% of people infected with the coronavirus may have persistent symptoms, including worrying changes in the brain and heart. Vaccination is thought to reduce the chances of a long Covid, even if it is not clear of how much.

“The long-term impacts on health care are unclear, but it is certainly worth taking them very seriously, as some people will have to struggle with the consequences for a long time,” said Bill Hanage, epidemiologist at Harvard TH Chan School. of Public Health.

Even a very small percentage of infected or vaccinated people who develop Covid would translate into millions nationwide.

While the goal is often to keep the health system from caving in to a surge, “we should also be concerned that our health system will be overwhelmed by the continuing health needs of a population with Covid for some time,” said Zoë McLaren, a health policy expert at the University of Maryland, Baltimore County.

There are still tens of millions of Americans without immunity to the virus and they remain vulnerable to both the short- and long-term consequences of the infection, said Dr. Tom Inglesby, director of the Center for Health Security at Johns Hopkins Bloomberg School of Public Health.

“Betting you’re in the 60 percent is a big bet,” he said. “For anyone who has not been vaccinated and boosted, I would take this new data as a direct message to do so or I expect the virus is likely to reach you if it isn’t already.”

Although cases are picking up again, particularly in the Northeast, the increase in hospitalizations has been minimal and deaths are still falling. According to the agency’s most recent criteria, more than 98 percent of Americans live in communities with a low or medium level of risk.

Even among those who are hospitalized, “we are seeing less oxygen consumption, fewer ICU admissions and, fortunately, we have not seen any increase in associated deaths,” said CDC director Dr. Rochelle Walensky. “We hope that the positive trends continue”.

The country has seen an approximately five-fold decline in PCR testing for the virus since Omicron’s peak, so tracking new cases has become difficult. But the reported count is much lower, about 70 times lower, said Dr. Walensky, reflecting “a true and reliable decline in our overall cases”.

New Omicron sub-variants, named BA.2 and BA.2.12.1, have supplanted the previous iteration, BA.1, which began circulating in the country in late November and sent cases at record levels within weeks.

“Obviously, even more have been infected now, because BA.2 will have infected some who have avoided it so far,” said Dr. Hanage said.

By February, three out of four children and adolescents in the country had already been infected with the virus, compared with one-third of seniors, according to the new study.

The fact that so many children carry antibodies can be of comfort to parents of people aged 5 and younger, who do not qualify for the vaccination, as many may have acquired at least some immunity through infection.

But Dr. Clarke urged parents to immunize children who qualify as soon as regulators approve a vaccine for them, regardless of their previous infection. Of children hospitalized with the virus, up to 30 percent may need intensive care, she noted.

Although many of these children also have other medical conditions, about 70 percent of cases of multisystem inflammatory disease, a rare consequence of Covid-19 infection, occur in otherwise healthy children.

“As a pediatrician and parent, I would absolutely appreciate having children vaccinated, even if they have been infected,” said Dr. Clarke said.

Some experts have said they are concerned about the long-term consequences, even in children who have mild symptoms.

“Given the very high rate of infections in children and adults that occurred earlier this year, I worry about the increase in long-term Covid cases as a result,” said Akiko Iwasaki, an immunologist at the University of Yale who is investigating the condition.

To measure the percentage of the population infected with the virus, the study relied on the presence of antibodies produced in response to an infection.

CDC researchers began assessing antibody levels in people at 10 sites at the start of the pandemic and have done so ever since. expanded that effort to all 50 states, the District of Columbia and Puerto Rico. Investigators used a test that was sensitive enough to identify previously infected people for at least one to two years after exposure.

The researchers analyzed blood samples collected from September 2021 to February 2022 for antibodies to the virus, then analyzed the data for age, gender and geographic location. The researchers specifically looked for a type of antibody produced after infection but not after vaccination.

Between September and December 2021, the prevalence of antibodies in the samples steadily increased by one or two percentage points every four weeks. But it rose sharply after December, rising nearly 25 points by February 2022.

The percentage of samples with antibodies increased from approximately 45% among children 11 years of age and younger and among adolescents 12-17 years of age to approximately 75% in both age groups.

According to the study, as of February 2022, around 64 percent of adults aged 18 to 49, around 50 percent of those aged 50 to 64, and around 33 percent of older adults had been infected.

The CDC may have underestimated the number of Americans who have been infected, said Dr. McLaren said.

Despite the record of high cases during Omicron’s peak, the reported statistics may not have captured all infections, because some people have few or no symptoms, may not have opted for testing, or may have tested themselves at home.

According to an upcoming CDC study, there may be more than three infections for each reported case, said Dr. Clarke said.

Noah Weiland contributed to the reporting from Washington.