Media coverage about COVID-19 antibody tests continues to dominate the news with dozens of companies announcing new solutions coming to market. Since the beginning of the pandemic, antibody tests have been touted as a way to identify people who are immune to COVID-19, and even as a way to reopen world economies by issuing digital “immunity passports” to people with detectable COVID-19 antibodies. However, a rising chorus of experts has cautioned against using antibody tests in this manner, citing the limited accuracy of many of the tests and the lack of scientific evidence linking antibody levels to COVID-19 immunity. We’re here to help you cut through all the noise and help you understand what antibody testing is, how it may be beneficial, and what its limitations are.
What are antibodies?
Antibodies, also known as immunoglobulins (abbreviated Ig), are infection-fighting proteins created by the immune system in response to the unique characteristics of the infectious agent. Over the course of an infection, the immune system produces different types of antibodies including IgM, which develops early in the immune response, and IgG, which develops later and can be a marker of immunity.
Because antibodies to a virus can only be produced if someone has been exposed to the virus (or to a vaccine, which doesn’t yet exist for COVID-19), the presence of antibodies to a virus is a good indicator that the person has been infected. IgM antibodies are produced by the body during an active infection, while IgG antibodies come later and typically signal the infection has passed. IgG antibodies may also indicate immunity, or resistance to reinfection with the same virus, as is the case for certain other viral diseases such as measles, hepatitis A and polio. We do not yet know whether IgG antibodies are indicative of immunity to COVID-19, but research is underway and we expect to have an answer to this question in the future.
What is a COVID-19 antibody test?
A COVID-19 antibody test, also known as a serologic test, detects the presence of antibodies specific to the causative virus, SARS-CoV-2, in a blood specimen. The most accurate antibody tests involve a laboratory technique called ELISA (Enzyme-Linked ImmunoSorbent Assay), and require a vial of blood to be sent to a diagnostic lab with specialized equipment.
Alternatively, handheld “point-of-care” test kits need only a sample of blood from a pricked finger and can give results within minutes. There are over 100 versions of this kind of test being offered worldwide, and the accuracy of these kits is highly variable, leading the World Health Organization to recommend against using them except for research purposes.
How is antibody testing different from PCR tests?
The vast majority of tests conducted for COVID-19 to date in the U.S. have been PCR (polymerase chain reaction) tests. PCR tests detect the presence of genetic material from the SARS-CoV-2 virus itself, and therefore can reveal whether someone has been infected early in the course of the illness, sometimes days before they’ve produced any antibodies to the virus. PCR is reasonably sensitive for detecting an active or very recent COVID-19 infection, and it remains the standard tool for identifying and isolating people with COVID-19 before they spread it to others.
PCR cannot be used to reliably determine whether someone has had an infection in the past, because individuals who have completely recovered from COVID-19 often no longer have any virus in their bodies and will therefore have a negative PCR test result.
Most PCR tests for COVID-19 use specimens collected from the nasal passages using a long swab gently inserted into a nostril. Saliva-based PCR tests are being evaluated as well.
What are the potential benefits of antibody testing?
Antibody testing can serve at least three important purposes. First, it can help identify people who are acutely infected with SARS-CoV-2, especially when paired with PCR testing. Antibody testing on its own is not accurate enough, since antibodies don’t develop until several days after an infection begins. But PCR testing isn’t perfect either, as it can miss up to 25% of acute infections. Combining antibody and PCR tests results may lead to improved sensitivity for detecting acute COVID-19 infection.
Second, antibody tests can help identify people who were previously infected with COVID-19 and have recovered. This is critically-important information for epidemiologists trying to understand how the virus spreads, how deadly the virus is, and how vulnerable a community might be to relaxation of social distancing rules.
Third, and most tantalizing, is the idea that antibody tests could confirm whether people are immune to COVID-19, either due to having recovered from the illness or due to vaccination (once a vaccine becomes available). Immune individuals would be able to interact with others without fear of spreading COVID-19 or becoming infected themselves, and would be able to serve essential roles in healthcare and in reopening the economy.
Most infectious disease experts think it’s likely that COVID-19 does induce some degree of immunity in those who recover from it, but this has yet to be proven. Whether immunity to COVID-19 might last a few weeks, a few years, or lifelong is also an open question.
What’s I AND MY DOCTORS CLINIC approach to antibody testing?
I AND MY DOCTORS CLINIC has started accepting patient requests for COVID-19 antibody testing.
I AND MY DOCTORS CLINIC has a dedicated team constantly evaluating the accuracy, speed, FDA approval status, availability and cost of antibody testing options. We will continue to provide updates to you and to our members as additional testing solutions have been properly clinically evaluated, vetted and approved for use.
