Thursday’s estimate is about 10 times more infections than the 2.3 million confirmed cases. Officials have long known that millions of people were unwittingly infected and that many cases are being lost due to gaps in evidence.
The news comes as the Trump administration works to allay national concern over the Covid-19 pandemic, as around a dozen states are seeing troubling increases in cases.
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The administration is also seeking to win its scientific experts back to the public as it tries to calm anxieties about the pandemic as states begin to reopen. Since mid-May, when the government began to emphasize the need to get the economy back on track, the panel’s public health experts have been much less visible than in the first weeks of the pandemic.
Twenty million infections means that approximately 6% of the nation’s 331 million people have been infected.
“It is clear that many people in this nation are still susceptible,” Dr. Robert Redfield, director of the Centers for Disease Control and Prevention, said in a call with journalists on Thursday. “Our best estimate right now is that for every case that was reported, there are actually 10 more infections.”
Previously, CDC officials and the country’s leading infectious disease expert, Dr. Anthony Fauci, said that up to 25% of infected people may have no symptoms.
“There are a huge number of people who are still vulnerable,” said Dr. Joshua Sharfstein, vice dean of the Johns Hopkins Bloomberg School of Public Health. “It is still a potentially lethal disease. It is a dice roll for everyone who gets the disease. Also, you roll the dice for other people to whom you can transmit the virus.”
The new estimate is based on CDC studies of blood samples collected nationwide, some by CDC and others from blood donations and other sources. Many infections went undetected in early tests, when supplies were limited and federal officials prioritized testing for those with symptoms.
Administration officials point to the new data to allay public concerns, claiming that while there have been significant spikes, they have the outbreaks well controlled. They argued that they were not trying to minimize a public health crisis, but said the nation is in a markedly different place with the virus now than when the United States last saw similar infection numbers in mid-April, when testing infrastructures they were weaker. Officials spoke on condition of anonymity Wednesday night to discuss the matter truthfully.
“This is still serious,” Redfield said in the call with reporters on Thursday. “But I ask people to recognize that we are in a different situation today than we were in March or April,” with more cases today in younger people who are not as likely to develop serious illness or die of infection, he said.
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President Donald Trump, who refuses to wear a face mask in public, has tried to minimize the risk. He told a crowd in Wisconsin on Thursday that the administration had done an “incredible job” fighting the virus, adding that “if we didn’t test, we wouldn’t have cases,” ignoring other indicators of the extent of the problem. such as the increase in hospitalizations in some areas.
Redfield said infection prevalence rates ranged from 1% in some areas of the West Coast to much higher in New York City.
Several independent experts said sampling methods and locations are key to interpreting the numbers.
Dr. Thomas Tsai, a health policy researcher at Harvard University, said 20 million seems reasonable, but “most of these estimates exist in a range” and it is important to know how broad it is.
“It is difficult to interpret this only from a single number and without context,” such as which locations were sampled and whether it was actually a random portion of a population or areas of low or high prevalence, which may bias the results.
Justin Lessler, a researcher at the Johns Hopkins Bloomberg School of Public Health, said 20 million infected “is about what you would expect based on the fatality rate” and the number of deaths that have occurred so far in the United States.
Despite the phasing out of daily White House coronavirus briefings, the administration has been closely monitoring the data on the spread of Covid-19 and has been deploying CDC teams to identify and stop outbreaks across the country.
A dozen states in recent weeks have seen a troubling rebound in new cases, as well as the most critical measure of the percentage of positive cases discovered in tests conducted. Seven states have seen more than 10% of the positive tests. And troublesome spikes in Sun Belt states have dominated news coverage in recent days, to the dismay of Trump administration officials.
Instead, they point to more nuanced data at the county level, which show positivity rates exceeding 10% in just 3% of the nation’s counties. However, they acknowledge that some of the areas with the highest transmission rates are generally the most populous, suggesting that tens of millions of Americans may be living in areas with stabbing infections.
As states reopen, the administration says it is up to local governors and officials to determine how to respond to the spikes. Republican Texas Governor Greg Abbott, for example, suspended steps to reopen and re-banned elective surgeries in some areas to preserve hospital space after the number of patients statewide doubled in two weeks.
CDC teams, authorities said, are working to track new outbreaks and strengthen protection measures such as social distancing and wearing masks in the hardest hit areas and to remind vulnerable populations to take extreme precautions. The administration says those efforts have helped curb new infections in North Carolina and Alabama, where they were deployed earlier this month.
One of the hardest hit areas is Phoenix, where Trump held an event on Tuesday with thousands of young attendees, almost all without a mask.
Officials say the nature of the outbreak is now different from that of months ago, when deaths exceeded more than 1,000 a day for weeks and hospitals expanded beyond capacity across the country. The new surge in positive cases, they said, is capturing what has been there for a long time. They say it’s only now popping up in the data because the U.S. has increased testing and surveillance.
Meanwhile, mortality data has steadily declined, as have hospitalizations at all but a few critical points.
For administration officials, that reinforces their hypothesis that millions of people unknowingly had the virus earlier this year. Until early May, federal guidelines prioritized testing for symptomatic individuals, those exposed to a positive case, and those in high-risk settings.
With the tests much more widespread now, authorities believe that 50% of new cases in Florida and Texas are among people age 35 and younger, and most of them are asymptomatic.
The United States is evaluating about 500,000 patients per day. On a per capita basis, the U.S. rate lags behind several other countries, including Spain, Australia, Russia, and Iceland, according to figures from Johns Hopkins University.
There is no scientific consensus on the rate of testing necessary to control the virus. But many experts say the United States should test approximately 1 million to 3 million people daily to detect new cases and prevent outbreaks. Administration officials said they expect to be able to perform 20 to 40 million tests per month starting this fall.
Testing is limited by the laboratory supplies needed to run the tests, but also by the lack of demand for testing in some areas.
Video: 20 million Americans have had coronaviruses, U.S. health officials say.