Antibodies are special proteins that an immune system typically makes during the course of an infection to help fight a germ and provide memory against a future reinfection. Tests for the presence of antibodies against COVID-19 (i.e. serology testing) are increasing in availability, due to the rapid development of assays by commercial manufacturers. Some people are asking if this could be helpful in diagnosing if they currently have COVID-19 infection or to determine if they’ve had the infection already and are now “immune.” What can a serology test result tell you? First, it may be more helpful to discuss what it can’t tell you:
- Serology tests may not diagnose a current COVID-19 infection.
Depending on the germ causing the infection and the type of antibody being produced, it may take days to weeks for an antibody response to be detected. When it comes to COVID-19, it may take at least 11-12 days after infection for antibodies to be detected. As a result, serology testing is not as helpful for diagnosing a current infection with COVID-19 but can tell you that you have had the infection at some point in the past. For some people who have trouble with forming antibody responses, such as those with immunocompromising conditions, a serology test might not be helpful for determining past infection.
- Serology tests cannot determine if you’re no longer contagious to COVID-19.
Many viruses continue to be “shed” (or be present and able to spread) in small amounts from respiratory secretions or saliva or feces for a period even after someone has recovered from an infection. It’s currently unknown how long someone is contagious after being infected with COVID-19. There have been some cases of persons who have recovered from COVID-19 and tested negative, weeks later testing positive again. We don’t know yet in those cases if the virus being detected from repeat testing is living virus capable of infection or fragments of dead virus. But there is no evidence at this time that antibody responses mean a person is no longer contagious with COVID-19. Persons who were recently infected and COVID-19 serology positive should still exercise caution to prevent spreading the virus to others.
- Serology tests cannot establish if you’re immune to COVID-19.
When it comes to other human coronaviruses that cause the common cold, reinfections tend to happen over the course of time. For some infections, the production of specific antibodies does not translate into future immunity. Right now, it’s unknown if those who were infected with COVID-19 and produced an antibody response are protected from future infection, and if so, for how long and to what degree they are protected.
- Serology testing may be useful when it comes to a certain type of experimental COVID-19 therapy. While there is still no proven effective treatment for COVID-19, some patients with severe infection may be treated with an experimental therapy using the COVID-19 antibody-enriched plasma of persons who have recovered from infection. Serology testing can help determine if a person might be eligible to donate plasma to someone else for this purpose.
- Serology testing can be used in public health studies to determine how much of a population has been infected with COVID-19. Determining the proportion of a population that has been infected with COVID-19 is an important data point used by public health and government officials to develop effective strategies in controlling the virus in the community.
Until more data emerge, Center City Pediatrics is not routinely ordering COVID-19 serology testing.
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