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About 1.7 million people have been infected by the coronavirus in the U.S., and scientists are finding evidence that the virus is both more common and less deadly than it first appeared. NPR's Jon Hamilton reports.
JON HAMILTON, BYLINE: The evidence is coming from places like Indiana. Nir Menachemi is the Chair of Health Policy and Management at Indiana University's Fairbanks College of Public Health. He says when COVID-19 first arrived in the state, he got a call from the governor's office. They wanted to know how many people had been infected and how many would die.
NIR MENACHEMI: It was really difficult to know for sure. And not just in our state, but frankly in any state.
HAMILTON: That's because health officials only knew about people who had been sick enough to get tested for the virus. And Menachemi says that number can be misleading.
MENACHEMI: It doesn't capture the vast number of people out there that might also be infected but not seeking medical care.
HAMILTON: So in late April, Menachemi led a study of more than 4,600 people statewide. Participants got two tests. The first was the standard test that looks for the virus itself. It shows whether you have an active infection. The second was a new type of test that looks for antibodies to the virus in a person's blood. It detects people who were infected but have recovered. Menachemi says the study showed that coronavirus had infected about 3% of the state's population, or 188,000 people.
MENACHEMI: That 188,000 people represented about 11 times more people than conventional selective testing had identified in the states to that point.
HAMILTON: And nearly half of infected people reported having no symptoms at all. Menachemi says it was like finally seeing the entire coronavirus iceberg instead of just the part above the water. And that allowed his team to calculate something called the infection fatality rate, the odds that an infected person will die. Menachemi says Indiana's fatality rate turned out to be about 0.6% or roughly 1 death for every 175 people who got infected.
MENACHEMI: That doesn't sound like a lot, but it's a very infectious disease that kills at a rate almost six times greater than seasonal flu.
HAMILTON: Still, it's much lower than earlier fatality estimates based on people who got sick. Some of those exceeded 5%. And the results in Indiana are similar to those of antibody studies in several other areas. New York, for example, appears to have a death rate between 0.5 and 0.8%. Caitlin Rivers is an epidemiologist at the Johns Hopkins Center for Health Security.
CAITLIN RIVERS: The current best estimates for the infection fatality risk are between a half a percent and 1%.
HAMILTON: She says a few studies have found much lower rates, but they have flaws.
RIVERS: They may have enrolled people who are more likely to have been infected than would have been ideal.
HAMILTON: For example, a study in Santa Clara, Calif. used Facebook to find volunteers, a tactic unlikely to attract a random sample. Rivers says calculating the overall infection fatality rate for the U.S. is very useful for researchers but less so for individuals.
RIVERS: So thankfully, children and young adults are at low risk of severe illness and death. But older adults are at quite high risk of severe illness and death.
HAMILTON: Studies suggest a healthy young person's chance of dying from an infection is less than 1 in 1000. For someone with health problems in their 90s, though, it can be greater than 1 in 10. And Juliette Unwin, a research fellow at Imperial College London, says that means different states in the U.S. should expect different infection fatality rates.
JULIETTE UNWIN: Places like Maine and Florida, we find that the infection fatality ratio is higher than in other places where the demographic is younger.
HAMILTON: Unwin is part of a large team in the U.K. that is monitoring both infection and mortality from coronavirus in the U.S. The team puts the infection fatality rate for the U.S. at somewhere between 0.7% and 1.2%.
Jon Hamilton, NPR News.
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