Covid-19 serology tests are the next critical phase of Covid-19 testing as they will be a powerful tool in determining a country’s immunity to the disease, which will allow governments to determine when social isolation could lessen and businesses re-open. As the global Covid-19 pandemic has progressed, testing has been of the utmost importance to determine how widespread the disease is, and hence how severe social distancing should be and if lockdown is required in order to “flatten the curve.” Countries, where social distancing has aided in the decline in new Covid-19 cases, are beginning to ask when normal life can resume. This is where serology tests come into play. The purpose of these Covid-19 serology tests is to detect antibodies in people exposed to Covid-19, and hence immunity to the disease.
The serology test uses a blood sample to identify antibodies and determine whether or not an individual has developed an immune reaction to the coronavirus. Antibodies are proteins secreted into the blood that bind to invading pathogens, such as the novel coronavirus, which then alerts the immune system to attack and destroy the virus. The purpose of a Covid-19 serology test is to determine if a patient once had the disease, and possibly whether they’re now immune.
Recently, there has been a lot of talk in the news cycle regarding the sensitivity and specificity of Covid-19 serology tests. These tests have a very high degree of sensitivity and specificity; the thing to consider, however, is what is known as positive predictive value (PPV). PPV is the probability that following a positive test result for Covid-19 antibodies, that individual truly had Covid-19. In other words, even with a 98% sensitivity and specificity for a Covid-19 serology test, some people will test positive for immunity to Covid-19 even though they do not have immunity to Covid-19 and were never infected; this is known as a false-positive result. Because of this, it is of the utmost importance that additional lines of evidence be used to determine if an individual has immunity to Covid-19, such as a previous positive test result to the reverse-transcriptase (RT)-PCR diagnostic Covid-19 test.
By and large, Covid-19 serology tests will be a powerful tool for population-level surveillance to inform governments of when enough people in the population have immunity to the disease, allowing for an easing in restrictions and re-starting of the economy.