Could the vaccine make me test positive for Covid-19?

Infectious disease diagnosis expert Dr. Matthew Binnicker explains the benefits and limitations of diagnostic testing as more people receive the Covid-19 vaccine.

More than 61 million doses of Covid-19 vaccine have been administered in the United States since December 2020. As more people are vaccinated, this means that the role of other mitigation measures, such as diagnostic tests, is starting to change.

Although the pace of vaccine manufacturing and distribution has increased, some experts estimate that it may be mid to late summer before most Americans have a chance to get vaccinated. Until then, and likely for months afterward, measures including masking and physical distancing will continue to be needed to prevent a resurgence in Covid-19. Diagnostic tests will continue to be an important tool, but it has certain limitations. Here are the answers to some common questions about Covid-19 vaccines and tests.

Could the vaccine test positive for Covid-19?

In the days and weeks after Covid-19 vaccines became available, health professionals observed that some vaccinated people tested positive on both PCR and rapid antigen tests (here’s a review on the different types of tests ). This immediately led patients and their doctors to question whether the vaccine can test positive.

The two Covid-19 vaccines (Pfizer / BioNTech and Moderna) currently licensed for use in the United States are mRNA-based vaccines. They do not consist of the entire genome of the SARS-CoV-2 virus, which causes Covid-19. Instead, these vaccines are made from a small region of the viral genome, which enters the host cell and “tricks” the cell into producing a specific viral protein (ie, the Spike protein) against which a response is generated. immune. RNA molecules are inherently unstable and are targeted by enzymes that can degrade RNA in a matter of hours. Therefore, mRNA-based vaccines will not make a Covid-19 PCR test positive. Similarly, these vaccines will not make rapid antigen tests positive, since the proteins produced after vaccination are not expressed in the respiratory (i.e. nasal) tract, which is sampled for Covid-19 PCR. or the antigen test.

So what does it mean when a vaccinated person tests positive? It is likely to indicate that they were infected with SARS-CoV-2 just before or after being vaccinated. Although current Covid-19 vaccines may not completely prevent a person from becoming infected, they are likely to reduce the incidence of asymptomatic infections and have shown a high level of efficacy in preventing symptomatic and serious illnesses.

Do I need an antibody test after vaccination to show that I am immune?

After vaccination, some people may question whether the vaccine was successful and are interested in a test to determine their immune status. Certain laboratory tests, called serological tests, are designed to detect antibodies that are generated in response to an infection. Although these tests can provide information on whether a person has been exposed to a virus in the past, they may not provide a reliable measure of a person’s immunity against the virus.

Serological tests for infectious diseases generally only tell us whether antibodies to a pathogen are present or absent, but do not provide specific details on “how muchThe antibody is present. Therefore, an individual may test positive for antibodies, but the level of antibodies detected by the test does not always correlate with the amount needed to protect them from getting sick. Similarly, a negative antibody test does not always mean that a person lacks immunity, as other parts of the immune system, such as T cells, can play a vital role in fighting an infection. Due to these limitations, routine antibody testing after Covid-19 vaccination is unlikely to be recommended.

Will we have to test for Covid-19 after the pandemic ends?

Covid-19 cases are declining in many parts of the world, likely due to a combination of strict precautionary measures, possible seasonal effects, and increased immunity against natural infection and vaccination. However, the emergence of new variants of SARS-CoV-2 has led to the clear possibility of another increase in Covid-19 cases. Whether or not there is a resurgence, at some point the pandemic will come to an end. When that happens, it is unclear what will become of Covid-19.

Will SARS-CoV-2 disappear completely or will it become an endemic cause of respiratory disease? Given that SARS-CoV-2 has reached every corner of the world and will continue to mutate over time, it is highly likely that Covid-19 will continue to cause outbreaks of mild to moderate respiratory illness, potentially with a seasonal pattern similar to influenza. Therefore, Covid-19 testing will likely remain important even after the pandemic is over. Healthcare providers will need to distinguish between Covid-19, influenza, and other causes of respiratory illness so that patients can be effectively treated and managed. In other words, Covid-19 is very likely to be with us, at least to some extent, in the next few years.

Full coverage and live updates on Coronavirus