What is ‘immunity theft’? How certain illnesses can leave you more vulnerable to other infections.

Having a COVID-19 infection can shore up your immunity to the virus, but can it also leave you more susceptible to getting sick with other illnesses? That's the theory laid out in a new scientific paper in JAMA Medical News and Perspectives, which looks at a possible tie between COVID and the recent surge in respiratory illnesses. The term “immunity theft” is being used to describe this phenomenon, although it hasn't been well-studied at this point. So what is immunity theft and how concerned about it should you be? Here's what infectious disease doctors have to say about it.

What is immunity theft?

It's important to point out that “immunity theft” is not a medical term. However, it's used to describe the theory that SARS-CoV-2, the virus that causes COVID-19, “steals” immunity, leaving some people who have had the virus more vulnerable to other infections.

That's different from the debated concept of “immunity debt,” which refers to having lowered immunity to a slew of bacteria and viruses stemming from a lack of exposure to those pathogens. (It's usually referred to in the case of COVID-19 lockdowns and how cases of the flu and RSV surged afterward.)

A study published in October in the journal Family Medicine and Community Health demonstrates the idea of immunity theft. For the study, researchers analyzed electronic health record data from 61.4 million patients in the U.S., including 1.7 million children up to age 5. The researchers found that kids who had COVID-19 were at a “significantly increased risk” of getting an RSV infection afterward compared to those who didn't have a previous COVID-19 infection.

“It's possible that your immune system is not normal after you have COVID-19,” Dr. Thomas Russo, professor and expert in infectious diseases at the University of Buffalo in N.Y., tells Yahoo Life. “The best example of that is in critically ill patients — they tend to get superinfections that can make them really ill.” However, Russo isn't a fan of using the word “theft” to describe immunity: “Immunity is something we develop and not something that is stolen or needs to be paid back,” he points out.

Dr. William Schaffner, an infectious disease specialist and professor at the Vanderbilt University School of Medicine, tells Yahoo Life that the idea of immunity theft is a “fascinating hypothesis,” but notes that there isn't a lot of science to back it up at this point.

Still, he says there is some data to suggest this could be real. “There is preliminary data from the field that would suggest that, if you've had a serious communicable disease, you may be more vulnerable to another infection for a period of time,” Schaffner says.

Can immunity theft happen with other health conditions?

Yes, say experts. People who get measles, for example, “lose immune protection against other infections” for a period of time afterward, Dr. Patrick Jackson, an infectious disease physician at UVA Health, tells Yahoo Life. “The measles virus infects immune cells that give us long-lasting immune memory and wipes them out," he explains. Schaffner agrees. “Measles infection clearly seems to have some impact on the immune system,” he says, noting that people can have more vulnerability to other infectious diseases for months after having measles.

The phenomenon can also happen with the flu, Russo says. “Post-influenza, you have a period of time where people may get better and then develop a bacterial superinfection,” he says. “That's because the influenza infection suppresses the immune response, making individuals more susceptible.”

But Russo says it's “less well sorted out” whether this is also the case with COVID-19. “Immunity theft is a real thing that can happen,” says Jackson. “But I haven't seen convincing evidence this is a significant issue with SARS-CoV-2.”

How to protect your immunity while recovering from COVID-19

If you've had COVID-19, Russo notes that you're likely protected from getting the virus — or, at least the same strain of the virus — for a few months afterward.

But Schaffner says it doesn't hurt to be aware that you may be more susceptible to other infections in the aftermath. Or, at the very least, know that you don't have immunity against those viruses. “Just because you've recovered from COVID doesn't mean you have protection against RSV and influenza,! he says.

If you're worried about getting sick after having COVID-19, Schaffner recommends wearing a mask in crowded indoor spaces and doing your best to avoid people who are coughing and sneezing.

Still, there's little evidence that having COVID-19 makes you more likely to get other illnesses. Because of that, Jackson says, you don't need to do anything different after having a COVID-19 infection. “There's nothing special people need to do when recovering from COVID that one wouldn't recommend for everyone,” he says. “Get exercise as tolerated if you're feeling run-down after a bout of COVID, eat a variety of fresh foods and don't smoke."