Indian-American Jay Bhattacharya in team which developed antibody tests that could be key to reopening country

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Here’s a twist: Discovering that hundreds of millions of Americans have been infected with the novel coronavirus might actually be good news.

It would indicate that lots of people have already developed immunity to the virus and could safely reenter society, and that the death rate from the virus is lower than originally suspected.

But right now, we have no idea just how many Americans have been infected with covid-19, the disease caused by the virus, and experienced only mild or no symptoms. While the United States has administered more coronavirus tests than any other country (not per capita) – nearly 1 million – that’s still a small fraction of the population, and it includes mainly people who experienced severe-enough symptoms to qualify for a test at all.

The answer to the crucial question of how many actual infections there are in the United States carries major implications for the Trump administration, governors and mayors, who have been forced to consider hugely consequential policies – for example, how long schools and businesses stay closed – with incomplete information about how widespread the virus truly is.

“I don’t know how you make policy without these numbers,” Stanford University researcher Jay Bhattacharya said. “They’ve had to make very difficult calls with very imperfect information.”

Researchers are racing for answers, using tests just now becoming available, with permission from the Food and Drug Administration. These serology tests – which detect disease-fighting antibodies – could help determine when and how to gradually reopen parts of the mostly shuttered U.S. economy, experts say.

If, for example, many Americans are discovered to have immunity, they could potentially start returning to work, school and other public settings soon. It would also indicate the U.S. fatality rate is much lower than the 1% to 2% scientists have estimated.

“The theory is that such testing could be used to divide the world into people who’ve had it and aren’t at risk anymore – and those who are,” The Washington Post’s Carolyn Y. Johnson said.

“Health-care workers with immunity could return to the front lines. Large employers could test their workers to find out who could return to work first. Health insurers might use the tests to tell members whether it is risky to go out into the world. People who know they have a level of immunity could help others.”

But if researchers find no such “herd” immunity, that could underscore a need to extend social distancing guidelines for some time. And it could indicate a higher fatality rate from covid-19.

Bhattacharya is among a group of researchers finalizing plans to administer thousands of finger-prick tests to residents of Santa Clara County, California, at drive-through sites this week. The group, which includes professors from Stanford and the University of Southern California, organized the Santa Clara testing project in a few weeks; such a project would normally take months to get off the ground. Bhattacharya told me that the group has received interest from researchers who are invested in getting better information about the extent of coronavirus infections in the United States.

At three testing sites in the area, volunteers will be able to drive by in their cars and receive a simple finger-prick test. Bhattacharya said he hopes to report some results early next week. He’s hoping to receive an additional 10,000 tests.

He says policymakers need a better understanding of the rate of infections before they can make informed decisions about how to enforce social distancing.

“We need this number, or else we’re flying blind,” Bhattacharya said.

The infection rate is one of several assumptions researchers use for models of how quickly U.S. infections could spread and how many deaths would result. They typically separate people into four groups: the non-infected, the infected who are sick, the infected who have recovered, and the infected who died. They estimate how quickly the virus is transmitted from person to person and how many people one person infects on average.

They also consider factors such as to what extent people are staying at home and when they started social distancing. States have taken a variety of approaches, some more stringent than others.

All of this means policymakers can choose from a wide range of projections as they respond to a fluid and rapidly changing situation on the ground.

Trump administration officials have focused on two models of how the pandemic could play out in the United States: one fairly dramatic projection from Imperial College London and another projection out of the University of Washington.

In modeling by Imperial College London, researchers projected that 1.1 million people in the United States could die with three months of social distancing measures, including closing all schools and universities, isolating infected patients and ordering household quarantines. They said deaths could be double that figure without such measures.

Administration officials have been citing a more-conservative model from the University of Washington’s Institute for Health Metrics and Evaluation, which projects that the virus will kill about 84,000 people in the U.S. over the next four months.

That projection was based on the assumption that people will continue practicing social distancing through May, professor Chris Murray told The Post. And Murray stressed that the projections will change as he gains access to more data throughout the country.

“It’s hard to predict the weather,” Murray told The Post. “It’s going to be hard to predict this epidemic, and so the best we can do is just keep updating with the best information available at the point that different leaders are making decisions.”

At Tuesday’s daily briefing, Deborah Birx, coordinator of President Donald Trump’s coronavirus task force, said she and other officials regularly check this model that Murray updates daily. She reiterated the administration’s estimate of 100,000 to 200,000 deaths in the United States, based on this model, even with what they describe as near-perfect compliance with social distancing edicts. And she warned Americans things could look worse if they don’t follow social distancing guidelines through April.

“Without continuation for the next 30 days, anything could change,” Birx said.