By: The Editorial Board – wsj.com – April 1, 2020

Tests that show immunity are crucial to beating Covid-19.

One of the great uncertainties in the coronavirus pandemic is how many people have been infected without knowing it or showing symptoms. Fortunately, there are now tests for that, and broadly deploying them will be critical to saving lives and getting Americans back to work.

Dozens of commercial and public health labs around the world are rolling out antibody tests that can show if an individual was recently infected with the virus and has developed immunity. When fighting a pathogen, the immune system produces proteins known as antibodies that bind to specific molecules known as antigens on the invader’s surface like a lock and key.

Antibodies circulate in the blood for weeks and even months after infection, providing resistance to another onslaught, though the immune system remembers how to produce them on demand. Vaccines work by instructing the immune system to make antibodies to shoot down pathogens before they proliferate.

Because antibodies linger in the blood, they are especially useful for determining if someone has been infected with the coronavirus. Some experts estimate that more than half of infected individuals show mild or no symptoms, though the true figure could be higher. Around three-quarters of people infected with flu viruses show mild or no symptoms.

Researchers and governments are now seeking to administer antibody tests to large groups of people to better gauge the virus’s prevalence in the general population. This would provide a more accurate assessment of lethality and allow exposed health-care workers with immunity to stay on the front lines.

Antibody data, as White House coronavirus coordinator Deborah Birx noted on Tuesday, might also show how widely the virus was circulating before testing expanded in March. It’s possible that many early cases in places like Seattle and New York went undetected during this year’s severe flu season.

Antibody tests would also let governments and individuals tailor their behavioral responses. Kids with antibodies could visit grandparents without worrying they might kill them. Governments could ease restrictions for those with immunity and focus on protecting those most at risk.

Researchers in Germany are preparing a mass study to test how many people are already immune, and those who are could receive “certificates of immunity” to return to work. Dutch health authorities are conducting antibody tests on tens of thousands of blood samples from healthy adults to discern its spread.

The U.K. has ordered 3.5 million antibody testing kits and intends to ship them to households after they have been verified. The goal is to enable more people to return to work faster. “Tests are being ordered across Europe and elsewhere and purchased in South-East Asia. This is widespread practice,” noted U.K. Director of National Infection Service Sharon Peacock.

Progress in the U.S. has been slower, though Governors including New York’s Andrew Cuomo, researchers and hospitals are eager to accelerate testing. The Food and Drug Administration last month issued emergency guidance permitting companies to launch antibody tests that have been internally validated as long as they cage results with numerous caveats to patients. These include that the test hasn’t been reviewed by the FDA, a negative result doesn’t rule out infection and “positive results may be due to past or present infection with non-SARS-CoV-2 coronavirus strains.”

Forty some companies have indicated that they plan to launch tests. But many are waiting for the government imprimatur of FDA approval and inoculation against lawsuits. Some caution about antibody tests is understandable. Tests must be specific and sensitive—i.e., detect an antibody particular to Covid-19 when present and not other antibodies. A false positive antibody result is more worrisome than a false coronavirus diagnosis since people who mistakenly believe they are immune could spread the virus.

This is why it’s important that antibody tests be validated for accuracy. But once they are, the FDA should ensure they can be distributed more quickly and broadly than the diagnostic tests have been.

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Source: Got Coronavirus Antibodies? – WSJ