CDC says coronavirus has infected more than half of Americans

By February, 60% of Americans, including 75% of children, had been infected with the coronavirus, federal health officials said Tuesday, another major milestone in a pandemic that continues to confuse expectations.

The highly contagious Omicron variant caused most of the casualties. In December 2021, when this variant began to spread, only half of people had antibodies indicative of a previous infection. according to new research from the Centers for Disease Control and Prevention.

While the numbers came as a shock to many Americans, some scientists said they expected the numbers to be even higher given the contagious variants that have swept through the country over the past two years.

There could be good news in the data, some experts say. Boosting the immunity of the entire population could provide at least partial protection against future waves. And this trend may explain why the surge now raging in China and much of Europe has been muted in the United States.

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

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

Administration officials also believe the data portends a new phase of the pandemic, in which infections may be common but cause less harm.

At a briefing on Tuesday, Dr. Ashish Jha, the new White House coordinator for Covid, said stopping infections “is not even a policy goal. The goal of our policy should be: obviously, to minimize infection as much as possible, but not allow people to become seriously ill.”

The average number of confirmed new cases per day in the United States — more than 49,000 as of Monday, according to the New York Times database — is comparable to levels last seen in late July, even as the number of cases has increased by more than by 50 percent over the previous month. Over the past two weeks, infectious disease experts have attributed this trend to new Omicron sub-variants.

Dr. Jha and other officials cautioned against complacency and urged Americans to keep getting vaccinated and boostered, saying antibodies from previous infections do not guarantee protection against the virus.

During the Omicron surge, infections rose most sharply among children and teens, according to a new study. Prior infections increased least among adults aged 65 years and older, who have the highest vaccination rates and may be most likely to take precautions.

“Evidence of previous Covid-19 infections has increased significantly among every age group,” Dr. Christy Clark, the agency’s researcher who led the new study, said at a briefing on Tuesday.

Widespread infection poses a worrying prospect: a potential increase in cases of long-term Covid, a poorly understood combination of lingering symptoms.

Up to 30 percent of people infected with the coronavirus may have persistent symptoms, including disturbing changes in the brain and heart. Vaccination is thought to reduce the chance of long-term Covid, though it’s not clear by how much.

“Long-term health effects are unclear, but certainly worth taking very seriously as some people will struggle with the effects for a long time,” said Bill Hanage, an epidemiologist at the Harvard T. H. Chan School of Public Health. Health.

Even a very small percentage of infected or vaccinated people who develop Covid will grow into millions across the country.

While the focus is often on making sure the healthcare system doesn’t buckle under a surge, “we also need to be concerned that our healthcare system will be overwhelmed by the ongoing needs of the population for long-term Covid healthcare,” said Zoe McLaren, health policy expert. health care University of Maryland, Baltimore County.

Tens of millions of Americans are still not immune to the virus, and they remain vulnerable to both the short and long-term effects of the infection, Dr. Tom Inglesby, director of the Johns Hopkins University Center for Health Security told Bloomberg. School of Public Health.

“Betting that you are in the 60 percent is a big gamble,” he said. “For anyone who hasn’t been vaccinated and hasn’t been revaccinated, I would take this new data as a direct message to do so, or expect the virus to most likely get you if it hasn’t already.”

Although the number of cases is rising again, especially in the northeast, the increase in hospitalizations has been minimal and the death rate is still declining. More than 98 percent of Americans live in low- or moderate-risk communities, according to the agency’s latest criteria.

Even among those who are hospitalized, “we’re seeing less oxygen use, less intensive care unit stays, and thankfully, we’re not seeing any increase in mortality associated with that,” said CDC director Dr. Rochelle Walensky. “We hope the positive trends continue.”

The country has seen a roughly five-fold drop in PCR tests for the virus since the peak of Omicron, making tracking new cases difficult. But the reported numbers are much lower, about 70 times lower, Dr. Walensky said, reflecting “a true and significant decline in our overall cases.”

The new sub-variants of Omicron, called BA.2 and BA.2.12.1, supplanted the previous iteration, BA.1, which began circulating in the country in late November and sent infections to record levels in a matter of weeks.

“Of course, even more are now infected, because BA.2 will infect those who have avoided it until now,” Dr. Hanage said.

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

The fact that so many children carry antibodies may be comforting to parents of children aged 5 and under who are not eligible for vaccination, as many of them may have acquired at least some immunity as a result of the infection.

But Dr. Clark urged parents to immunize eligible children as soon as regulatory authorities approve a vaccine for them, regardless of their prior infection. She noted that among children hospitalized with the virus, up to 30 percent may need intensive care.

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

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

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

“Given the very high proportion of infection among children and adults that occurred earlier this year, I’m worried about an increase from long-term cases of Covid,” said Akiko Iwasaki, an immunologist at Yale University who studies 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 the infection.

CDC researchers began assessing antibody levels in people at 10 locations early in the pandemic and have since extended this effort to all 50 states, the District of Columbia and Puerto Rico. The researchers used a test sensitive enough to identify previously infected people for at least one to two years after infection.

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

Between September and December 2021, the prevalence of antibodies in samples steadily increased by one to two percentage points every four weeks. But it rebounded sharply after December, up almost 25 points by February 2022.

The percentage of samples with antibodies has risen from about 45 percent among children aged 11 and under and among adolescents aged 12 to 17 to about 75 percent in both age groups.

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

Despite record high infection rates during the Omicron surge, reported statistics may not have covered all infections because some people have little to no symptoms, may not have opted for testing, or may have tested themselves at home.

According to Dr. Clark, there could be more than three infections for every reported case, according to one upcoming CDC study.

Noah Weiland provided a report from Washington.