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Sixty percent of Americans, including 75 percent of children, had contracted the coronavirus by February — another major milestone in the pandemic that continues to surprise expectations, federal health officials reported Tuesday.

The highly contagious Omicron variant was responsible for most of the toll. Since the variant began spreading in December 2021, only half of people had antibodies that indicated earlier infection. according to new research From the Centers for Disease Control and Prevention.

While the numbers are shocking to many Americans, some scientists said they expect the numbers to be even higher, given the infectious variants that have spread across the nation in the past two years.

Some experts said there may be good news in the data. Gaining population-wide immunity may offer at least a partial shield against future waves. And the trend may explain why the volatility that is now roaring in China and many countries in Europe has been muted in the US.

A high percentage of previous infections may mean that there are now fewer cases of life-threatening illness or death compared to infections. “We’re going to see a shift towards less severe disease and clinically mild disease,” said Florian Krammer, MD, an immunologist at the Icahn School of Medicine at Mount Sinai in New York.

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

Management officials also believe the data point to a new phase in the epidemic where infections may be common at times but are less damaging.

The new Covid coordinator of the White House, Dr. Ashish Jha said at a news conference Tuesday that stopping infections “is not even a policy goal.” The goal of our policy should obviously be: to minimize infections where possible, but to ensure that people do not become seriously ill.”

The average number of new confirmed cases per day in the United States – more than 49,000 as of Monday – according to the New York Times database. comparable to levels last seen at the end of Julyeven as a case increased by more than 50 percent A trend over the past two weeks that infectious disease experts have attributed to new Omicron subvariants.

Dr. Jha and other officials warned against complacency and urged Americans to continue getting vaccinated and booster shots, saying that antibodies from previous infections do not guarantee protection from the virus.

Infections increased most sharply among children and adolescents during the Omicron surge, according to new research. Previous infections increased least among adults 65 and older, who had the highest vaccination rates and were most likely to take precautions.

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

The widespread infection raises a troubling prospect: a potential increase in long-term Covid cases, a poorly understood constellation of ongoing symptoms.

Up to 30 percent of people infected with coronavirus may have persistent symptoms, including alarming changes in the brain and heart. Vaccination is thought to reduce the long-term risk of Covid. though unclear how much.

“The long-term effects on health care aren’t clear, but they’re definitely worth taking very seriously, because some people will struggle with the consequences for a long time,” said Bill Hanage, an epidemiologist at the Harvard T.H. Chan Public School. Health.

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

While the focus is often on preventing the healthcare system from collapsing under a surge, “We must also be concerned that our healthcare system will be overwhelmed by the continuing healthcare needs of a population with long-standing Covid-19,” said Zoë McLaren. Health policy expert at the University of Maryland, Baltimore County.

Johns Hopkins Bloomberg Center for Health Security director Dr. Tom Inglesby said that there are still tens of millions of Americans who are not immune to the virus, leaving them vulnerable to both the short-term and long-term consequences of infection. School of Public Health.

“Betting that you’re in the 60 percent is a big gamble,” he said. “For anyone who hasn’t been vaccinated and not boosted, I’d take this new data as a direct message to do it, or wait for the virus to probably catch you if it hasn’t been caught yet.”

While cases are on the rise once again, especially in the Northeast, the increase in hospitalizations is minimal and deaths are still falling. More than 98 percent of Americans live in low- or moderate-risk communities, according to the agency’s latest criteria.

CDC’s director, Dr. Even among those hospitalized, “we see less oxygen use, fewer ICU stays, and fortunately we haven’t seen any increase in deaths associated with these,” said Rochelle Walensky. “We are hopeful that positive trends will continue.”

The country has seen a nearly five-fold drop in PCR testing for the virus since the Omicron summit, making it difficult to track down new cases. However, saying that the reported number is much less, about 70 times lower, Dr. Walensky said there was “a real and credible drop in our overall cases.”

Omicron’s new sub-variants, designated BA.2 and BA.2.12.1, replace the previous iteration BA.1, which began circulating in the country in late November and had cases hit record highs within weeks.

Dr. “Of course now it has infected even more, because BA.2 will have infected those who have so far avoided it,” Hanage said.

By February, three out of four children and adolescents in the country had already contracted the virus, compared to one-third of older adults, according to the new study.

The fact that so many children have antibodies can provide comfort to parents of children aged 5 and younger who are not eligible for the vaccine, as most may have acquired at least some immunity through infection.

However, Dr. Clarke urged parents to vaccinate eligible children as soon as regulators approve a vaccine, regardless of previous infections. He noted that 30 percent of children hospitalized with the virus may need intensive care.

While 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 healthy children.

Dr. “As a pediatrician and parent, I strongly support vaccinating children, even if they are infected,” Clarke said.

Some experts said they were concerned about the long-term consequences, even in children with mild symptoms.

“Given the very high rate of infection in children and adults earlier this year, I am concerned about the increase in long-term Covid cases,” said Akiko Iwasaki, an immunologist at Yale University who has studied the situation.

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 in 10 regions early in the pandemic and have since expanded this effort To all 50 states, the District of Columbia and Puerto Rico. The researchers used a test sensitive enough to detect previously infected people for at least one to two years after exposure.

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

Between September and December 2021, the prevalence of antibodies in the samples increased by 1-2 percentage points every four weeks. However, it jumped sharply after December and increased by about 25 points by February 2022.

The percentage of samples with antibodies increased from about 45 percent in children 11 years of age and younger and adolescents 12 to 17 years old to about 75 percent in both age groups.

According to the study, by February 2022, about 64 percent of adults aged 18 to 49, about 50 percent of those aged 50 to 64, and about 33 percent of older adults were infected.

Despite record high cases during the Omicron surge, the statistics reported may not have caught all infections because some people have few or no symptoms, may not have chosen to be tested, or may have tested themselves at home.

Dr. Clarke said there could be more than three infections for every reported case, according to an upcoming CDC study.

Noah Weiland Contributed to reports from Washington.