NEW YORK (Reuters Health) – Given the little we know about the immune response to SARS-CoV-2, it is still unclear what role serological tests for antibodies to viruses should play, according to comments.
“There is too much uncertainty in serological testing to play any role in current disease management or policy,” said co-author Dr. Richard Torres from the Department of Medicine Laboratory of Yale University’s New Haven, Connecticut, Faculty of Medicine, told Reuters Health by e-mail.
Various real and self-proclaimed experts, as well as politicians and other professionals, have advocated testing of SARS-CoV-2 antibodies to identify individuals who have developed immunity and have the potential to safely reenter the workplace despite the presence of the virus.
Dr. Torres and Dr. Henry M. Rinder considers whether SARS-CoV-2 serological tests are safe for this purpose in their online American Journal of Clinical Pathology editorial.
What we know now, they say, is that people with symptomatic SARS-CoV-2 infection will generally not have antibodies detected against SARS-CoV-2 within the first week of symptoms. Most people who are hospitalized with confirmed SARS-CoV-2 infection will have IgG antibodies that can be detected 14 to 28 days after symptom onset.
However, it is still unclear whether the presence of antibodies against SARS-CoV-2 provides protection, especially in seriously ill patients. About a third of patients infected with SARS-CoV-2 who develop antibodies during hospitalization appear to lack antibodies that neutralize the virus in plaque growth tests, the standard test for antibody effectiveness.
In addition, the presence of antibodies does not guarantee that a person is not contagious; there may still be release of active viruses, especially if antibodies are not neutralized.
The quality of serological tests can also be a problem. Although there is minimal cross-reactivity with 4 common non-SARS-CoV-2 coronaviruses, validation studies are still needed to eliminate the risk that some tests may only reflect previous exposure to the common cold.
Finally, almost nothing is known about the pattern of antibody response to SARS-CoV-2 in asymptomatic individuals or the correlation of antibody responses with susceptibility to re-infection.
“The best test for susceptibility to infection from SARS-CoV-2 will depend heavily on a better understanding of the pathophysiology of the disease,” Dr. Torres. “In particular, we need to know whether antibodies are a requirement for preventing symptomatic disease or whether other aspects of the immune system can survive without relying on antibodies. And if we really need antibodies, how many antibodies do we need and which parts of the virus need to be directed. ”
“The best ‘test’ may still be a simple symptom screen,” he said. “Meanwhile, monitoring individuals with direct nucleic acid testing for SARS-CoV-2 viral load (and symptom screening) and then characterizing the rate of recovery and re-infection (if it does) is likely to help sort out the risk of vulnerability in each individual and population in generally. ”
Dr. Torres concluded, “We cannot assess the value of serology until it is actually paired with nucleic acid testing and long-term follow-up in well-designed research, so it shouldn’t be used for policy. We don’t need to test everyone to get the answers we need. Smart sampling, good data collection, and strong statistical analysis will give us the information we really need. ”
Bobbi S. Pritt, a clinical microbiologist involved in COVID-19 responses at the Mayo Clinic, Rochester, Minnesota, told Reuters Health via email, “Neutral antibody tests are needed to determine whether antibodies produced by certain individuals will actually protect them from reinfection with SARS-CoV-2. Serological tests cannot confirm whether a person is no longer contagious. However, one or more negative PCR tests for SARS-CoV-2 can be used for this purpose, together with resolution of clinical symptoms. ”
“There are many warnings for serological testing,” he said. “Unfortunately, serology cannot be used as a reliable immunological passport to send people back to work.”
Patrick S. Sullivan, epidemiologist from Emory University Rollins School of Public Health, Atlanta, Georgia, who is currently testing a patient’s ability to collect enough specimens for SARS-CoV-2 virus detection and serology, told Reuters Health by email, ” One issue that will become important in clinical practice is the understanding that in populations with low prevalence, such as screening for populations regardless of symptoms, that many positive results on antibody tests may be false positive results. So a population-based screening program will provide some information about immunological experiences with viruses among that population, but for each individual participant in the study, the meaning of a positive test might not be clear. ”
“I am a public health officer, so I think I will make the case that we should focus more on population-based studies that will give us unbiased estimates of the level of SARS Co V2 exposure in the population, rather than convenience. samples or research intended to inform putative immunity or return to work policies, “he said. “In many ways, trends over time in the prevalence of antibodies in the population are more likely to provide credible information about the condition of society and the potential for herd immunity, compared to looking at individual test results and trying to decide which individuals might become immune.”
“We need to have an appropriate level of humility about what we don’t know about the meaning of current generation antibody tests, especially when trying to interpret the clinical significance of certain tests for certain patients,” Dr. Sullivan.
SOURCE: bit.ly/2xqoyNw American Journal of Clinical Pathology, online April 23, 2020.
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