COVID-19 Q&A: Antibodies and natural immunity are difficult to measure

December 14, 2021
Dr. Christine Hahn, Public Health medical director and state epidemiologist

How long do the antibodies protect you from COVID-19?

Nobody knows if there is a certain level of antibody, or certain types of antibodies (such as neutralizing antibodies) that can predict protection, although antibody levels are used in clinical trials as a way to estimate protection from the vaccines. Antibody levels indicate some immune response to the vaccine. Some studies suggest that at least for the same variant, protection after infection may last for months, but it’s not certain. Some people who get COVID-19 do get it again even after developing antibodies, so protection is not guaranteed.

That’s why we encourage all Idahoans to consider getting vaccinated and boosted. It’s the best protection we have against serious illness and death.

Do we know how many people have had COVID-19 more than once?

Some cases of COVID-19 reinfection have been reported, but they continue to be rare. Based on what we know from similar viruses, some reinfections are expected. Unfortunately, it appears that reinfection is more common in areas where Omicron has appeared, so having had a previous infection with another variant may not be as protective against this new variant.

Viruses are constantly changing, including the virus that causes COVID-19. These changes occur over time and can lead to new variants that may have new characteristics. Vaccines continue to reduce a person’s risk of getting the virus that causes COVID-19 and are highly effective against severe illness.

Results from this study found that among those who had COVID-19, getting vaccinated after COVID-19 infection greatly lowered the chance of getting it again. “Among Kentucky residents infected with SARS-CoV-2 in 2020, vaccination status of those reinfected during May–June 2021 was compared with that of residents who were not reinfected. In this case-control study, being unvaccinated was associated with 2.34 times the odds of reinfection compared with being fully vaccinated.”

How soon you can get the vaccine after you have been diagnosed with COVID-19?

People with COVID-19 who have symptoms should wait to be vaccinated until they have recovered from their illness and have met the criteria for coming out of isolation; those without symptoms should also wait until they meet the criteria before getting vaccinated. This guidance also applies to people who get COVID-19 before getting their second dose of vaccine.

People who have had a COVID-19 exposure should not get vaccinated until their quarantine period has ended to avoid possibly exposing healthcare workers and others during the vaccination visit. This recommendation also applies to people with a known COVID-19 exposure who have received their first dose of an mRNA vaccine but not their second.

Anyone who receives monoclonal antibodies for COVID-19 should wait for 90 days before getting vaccinated.

Dr. Christine Hahn is Idaho’s state epidemiologist and the Division of Public Health’s medical director. She is board certified in infectious disease and works in the Family Medicine Residency of Idaho’s tuberculosis clinic twice monthly. She also serves on CDC’s Advisory Committee on Immunization Practices, and since late February 2020, has been focusing almost solely on responding to the coronavirus pandemic.

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