An important step towards reducing social distancing guidelines and allowing individuals to return to work is to determine what type of immunity previously infected individuals are gaining against COVID-19. To help figure this complex situation out, researchers and governmental agencies, such as the FDA, are suggesting the use of immunoglobulin tests. These tests determine if the serum of the blood contains antibodies, specifically IgM and IgG, against COVID-19. While this form of testing would not be beneficial in diagnosing, it is helpful to epidemiologists in creating a more accurate picture of how the virus is affecting the overall population. It also helps them gain an idea of what form of immunity is given to individuals that have been infected with COVID-19. This is extremely useful in determining the overall timeline for social distancing.
As mentioned above, these immunoglobulin tests determine if IgM and IgG antibodies against COVID-19 are present in the serum of the blood. IgM antibodies are the first form of antibody to be produced against an infection and are a more general form of protection. They are usually less effective than other antibodies in binding to antigen, but they are important in creating an initial response. Thus, if a person tests positive for IgM antibodies alone, they would most likely be in the initial stages of infection. IgG antibodies, on the other hand, are generally produced a few days after the initial infection, peaking 28 days after. These antibodies provide a more specific and effective response, as they are better able to bind antigen, which is why it takes several days for them to start being produced. Thus, if an individual tests positive for IgG alone, they are most likely in the later stages of infection, or are past the infection period of the virus. These antibodies also have a long half-life, providing lasting infection to the virus. If a person tests positive for IgG, this could mean possible immunity to the virus, at least for a short amount of time. If a person has these antibodies, it is unlikely that they could carry and transmit the virus, due to quick opsonization and phagocytosis of the virus, although there is still much research that needs to be conducted before a blanket statement regarding immunity can be made.
One important factor researchers need to focus on before this “certificate of immunity” can be given to individuals, effectively allowing them to return to their job and society, is how much immunity these antibodies really give. According to leading immunologists, different viruses can be placed on an immunity spectrum based on how long-lasting the immunity to that virus is. On one end are viruses like varicella-zoster, which produce antibodies that provide life-long immunity. At the other end are viruses like HIV, which seem to produce antibodies that have almost zero effect on the virus. By looking at other novel coronaviruses and common cold-associated coronaviruses, it seems that immunity should last for at least a year, but will most likely not provide immunity for longer than a few. The longest known immunity for a coronavirus is 8 years, although it is unlikely that this strain will provide that long of an immunity.
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