If you’ve recently recovered from COVID-19, you’re probably wondering how long you’ll be immune to infection. As we continue to navigate how to handle new variants and stay safe throughout the pandemic, it’s important to understand how immunity works.
There are different types of immunity: Infection-induced immunity, vaccine-induced immunity and hybrid (a combination of the two). We spoke to doctors to learn more about COVID immunity and what to expect after infection. Here’s everything you need to know.
How Long COVID Immunity Lasts After Infection
Dr. Jason Gallagher, MD, infectious disease expert, a Clinical Professor at Temple University’s School of Pharmacy and a Clinical Pharmacy Specialist in Infectious Diseases at Temple University Hospital says that ‘it depends.’ It seems that high levels of antibodies last for at least three months before they start to drop. But when they do drop, they can still be effective, especially against variants that are similar to what a person was infected with previously. Also, antibodies aren’t the only component of the immune system that helps after infection, they’re just one of them and the easiest to measure.
Some immune responses to the SARS-CoV-2 virus that causes COVID-19 can be detected for a long time after infection—at least a year, Dr. Erica Johnson, MD, Chair of the Infectious Disease Board at the American Board of Internal Medicine, explains. However, that doesn’t mean that you are protected from getting infected again for that long, and in fact, what we have been seeing with the omicron lineage is that many people with prior infection with earlier variants or prior vaccination against COVID-19 still developed infection with an omicron subvariant.
This is in part because there are different immune responses to the virus that all play a different role in protection from future infection, and some parts of this immune response may not be as robust as other parts depending on the person, the nature of their infection including the variant with which they were infected, and their prior history of vaccination and/or infection, Dr. Johnson adds.
How Does Natural Immunity Work After COVID Develops?
After infection, many patients develop antibodies that bind a specific part of the virus needed for it to infect cells. These antibodies help reduce the chance of reinfection with future exposures to the virus. Other parts of the immune system also develop specific responses to the virus that the immune system can recall in the event of a re-exposure to the virus, Dr. Johnson states.
These same types of responses happen after vaccination, too, and in fact, vaccination is designed to mimic what would happen if the body were exposed to the virus in the first place.
How Protective Is Hybrid Immunity?
Each time you are exposed to a dose of vaccine or have a natural infection, your immune system recalls its prior exposure to the virus and is boosted. With the first few doses of vaccine alone, this boosted response in many people would wane after several months. But the combination of being up to date with vaccination and having had a natural infection has been demonstrated to provide a more durable immune response than vaccination alone, Dr. Johnson explains.
In fact, one study in the New England Journal of Medicine showed that immunity remained high for longer than a year after infection in a study of healthcare workers in the UK who had an infection and two doses of mRNA vaccine.
"Hybrid immunity" seems to be the most durable type, but it comes with the obvious downside that one has to develop COVID-19 before one can get it, Dr. Gallagher states. Either pathway to getting it, whether acquiring infection and then being vaccinated or being vaccinated and then infected, seems to work.
It is likely because, until recently, the vaccines have only taught our body how to recognize one type of SARS-CoV-2, and while they taught it really well (remember the vaccines were over 90% effective at preventing infection), the virus has since changed many times since then. The new, bivalent booster vaccines, teach immunity to both the ‘original’ SARS-CoV-2 and an omicron strain, and data suggests they protect better against both. Hybrid immunity works the same way, Dr. Gallagher adds.
Also, receiving a vaccine after acquiring an infection boosts responses effectively beyond the window that becoming infected provides.
Dr. Erica Johnson, MD, Chair of the Infectious Disease Board at the American Board of Internal Medicine
Dr. Jason Gallagher, infectious disease expert, a Clinical Professor at Temple University’s School of Pharmacy, and a Clinical Pharmacy Specialist in Infectious Diseases at Temple University Hospital