Antibody tests seen as avenue to reopening

Some states are preparing novel coronavirus antibody tests to gauge the extent of infection and to help formulate a policy to reopen society and the economy.

Tennessee Health Commissioner Dr Lisa Piercey announced on Monday that the state's plan for COVID-19 antibody testing will begin in two phases, starting with the testing of 10,000 healthcare workers across the state.

In Arizona, two Phoenix companies are offering drive-through antibody testing that can indicate whether a person has been exposed to the virus and developed antibodies against it.

New York Governor Andrew Cuomo initiated a statewide antibody-testing survey more than a week ago.

The governor said on Tuesday that an antibody test of 7,500 people found that a quarter of New York City residents may have already survived the virus, although that doesn't mean they are immune, according to an AFP report.

Some antibody studies have suggested that the pandemic is much more widespread than the confirmed cases suggest.

A Stanford University antibody study has found a higher rate of coronavirus infection than previously believed. In the study, the preliminary results of which were released about a week ago, 3,300 residents of Santa Clara County in Northern California were tested, and an estimated 2.49 to 4.16 percent had been infected with the novel coronavirus by April 1.

An extrapolation of that ratio would represent between 48,000 and 81,000 people, which is 50 to 85 times the county's official number of 956 confirmed cases by that day.

Antibodies are produced by the immune system when the body is invaded by a virus. Scientists hope to use the test to estimate the extent of COVID-19 infections, because there is a report that 30 to 50 percent of infected populations have zero or minor symptoms, and there has been a shortage of tests in many places.

However, the Stanford study was not peer-reviewed. Its participants were recruited through social media, with white females overrepresented, raising questions about the data sampling.

In Los Angeles, the University of Southern California (USC), in partnership with the Los Angeles County Department of Public Health, has launched a similar study to test LA residents for the COVID-19 antibody, according to a USC report.

Neeraj Sood, a professor of health policy and vice-dean for research and faculty affairs at the USC Price School of Public Policy, is leading the study, which will sample 1,000 people.

Sood said the sample methodology employed will ensure that factors such as age, race and sex are part of the random selection.

"We need to test a representative sample of the general population to understand basic facts about the disease: how widely the virus has spread, the mortality rate associated with infection, and what potential immunity might be across a population," Sood said.

Antibody tests also are being conducted in Miami-Dade County, Florida, and San Miguel County, Colorado.

However, some healthcare experts have cautioned not to overly rely on antibody tests to make assumptions about immunity and reopening.

The first issue is the quality of available antibody tests. The Food and Drug Administration (FDA) has allowed about 90 companies to sell antibody tests not yet vetted as a pandemic emergency measure. The FDA, however, has warned that some of those businesses are making false claims.

Health officials have found the accuracy of some tests are very low, according to The New York Times.

"The problem is that these are tests that need to be validated and calibrated, and many of the tests out there don't do that. So even though you hear about companies flooding the market with these antibody tests, a lot of them are not validated," Dr Anthony Fauci, a member of the White House Coronavirus Task Force, said recently during an interview on Good Morning America.

Another issue is the possibility that a person with antibodies could be infectious. A German study, published in Nature, found that viral RNA of COVID-19 declines slowly after antibodies are detected in the blood. The presence of viral RNA could mean that the person with COVID-19 antibodies is still shedding the infectious virus.

"There's an assumption — a reasonable assumption — that when you have an antibody that you are protected against reinfection, but that has not been proven for this particular virus. It's true for other viruses," Fauci said.

"We don't know how long that protection, if it exists, lasts. Is it one month? Three months? Six months? A year?

"Unless that test has been validated and you can show there's a correlation between the antibody and protection, it is an assumption to say that this is something that we can work with," Fauci said.

However, Sood believes that antibody tests can help shape policy by providing insight into the extent of infection and the death rate.

"If you look at a mortality-rate calculation, the numerator is the number of deaths, and the denominator is the number of infections," Sood said.

"The larger the denominator is, the lower the mortality rate. This rate matters because it informs us about the risk. It also can inform policymakers' decisions on whether to keep stay-at-home orders and social distancing measures in place and for how long."