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At that point, San Miguel County was, like everywhere else in the United States, having trouble getting tests for every patient who needed one. This particularly worried Sharon Grundy, the county medical officer, because Telluride had so many visitors coming and going. “We’re a high-risk area because we are a resort community,” she told me. (A group of skiers visiting another Colorado resort town, Vail, ended up seeding a coronavirus outbreak in Mexico.) The county was able to test some people through the state health department and a commercial lab, and got its first positive result on Friday. But when I spoke with Grundy on Friday, she also said the whole county had only two swabs left. “It’s not just us,” she hastened to add. “It’s the whole country.”

Without testing, San Miguel County’s health workers would be unable to track the virus’s spread. They would be, to use the words of the World Health Organization’s director-general, fighting “a fire blindfolded.” So United Biomedical’s offer to donate the kits came as a relief. “This gave us some hope,” Grundy said.

United Biomedical’s COVID-19 test is different from those typically being run on nasal swabs collected around the country. Those tests use a technique called RT-PCR to look for the virus’s genetic material in a patient’s nose and throat, but United Biomedical’s test requires a blood draw. It uses a different technique, called ELISA, to look for antibodies, the proteins the immune system makes to neutralize the virus. Antibody tests, also known as serological tests, don’t always pick up early viral infections, but they can tell if someone has ever had a particular virus—maybe even if they were asymptomatic.

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For this reason, scientists all over the world have been pushing antibody tests as a way to study the true scope of the coronavirus pandemic. If serological testing can find asymptomatic carriers of COVID-19, it can also clarify the disease’s transmission and fatality rate. Testing a whole population—say, a whole county—would give epidemiologists a snapshot of everything going on in one place. “Any sort of population-based study is really interesting,” says Caitlin Rivers, an epidemiologist at Johns Hopkins University. And while it’s unclear how long immunity to COVID-19 lasts, she says, it could allow people who are immune to go back to their normal lives.

Hu said that United Biomedical started working on an antibody test back in January, as the outbreak got serious in China. The company had developed a very similar test for SARS in 2004. Its scientists could apply that expertise to COVID-19, but they needed blood samples from COVID-19 patients to confirm that the test indeed detects antibodies against the virus causing the disease. The company’s existing connections to China and Taiwan helped it get patient samples quickly. “We were actually able to ship tests to ground zero in Hubei, Shanghai, Beijing, and Taiwan,” Hu said.