Minnesota is starting to ramp up its testing of symptomatic people to the goal of 20,000 per day. On Monday 2,400 symptomatic people were tested -- more than double a week ago. Officials say it will take time to fully get up to speed and they’re working out logistics. It’s also seen in the numbers: Minnesota’s department of health announced the state’s “by far largest increase” of lab-confirmed cases of coronavirus -- 365 -- Tuesday. The total is 4,181.
But that’s molecular tests. Serological, or antibody testing, long held as a source of hope to get more of the economy back open, still contains many unknowns.
The lack of certainty revolves around the virus itself -- is there is protection and if so, how long does it last? -- and the tests -- which vary in accuracy.
It takes time to build up antibodies and the timing of the test could determine the outcome. Not many of the 100 or so on the market determine viral neutralization, and even with reliable specificity and sensitivity, accuracy will vary with how many people have been exposed. Tests are not 100% sensitive or 100% specific, according to state epidemiologist Dr. Ruth Lynfield, which could lead to false positives.
Lynfield makes the comparison to the measles and the flu; immunity with the latter, which is the same type of virus as coronavirus, is short-lived.
“We don’t know what it means,” Lynfield said. “We don’t know if somebody has antibody presence, we cannot say that you are not going to get infected again, because we don’t know that. We don’t know if you get infected again, you may still be able to shed virus and transmit to other people.”
Lynfield says the way serological tests can be helpful now is finding convalescent plasma donors and determining the scope of the infection in Minnesota, but not “individual decision-making.”
“We don’t know what that proportion of population-based immunity is,” she said. “It depends on how transmissible it is. It depends on how long-standing and effective the protective immunity is. Some scientists have estimated that it needs up to 80 or 90 percent, and if that is the case, we really hope that we will have an effective vaccine because that will be the most effective way to ensure high rates of immunity in the population and that the virus does not continue to circulate.”
She adds that serological testing or the presence of antibodies does not mean someone can stop social distancing.
