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I had COVID-19 when I got my booster... do I need another one?

MIT Medical answers your COVID-19 questions. Got a question about COVID-19? Send it to us at CovidQ@mit.edu, and we’ll do our best to provide an answer.

I got my COVID-19 booster on Monday of last week. I had a slightly scratchy throat at the time, but I thought it was due to the dry winter air. I felt really sick when I woke up on Tuesday but chalked that up to side effects from the shot — until later that afternoon, when the friend I’d had dinner with on Saturday night called to tell me she was sick and had tested positive. I immediately took a rapid test. Sure enough, it was positive.

One week later, I’m finally starting to feel better, but now I’m worried. I know the CDC tells you not to get a shot if you are sick, but I was obviously infected with the virus when I got my booster, even though I didn’t realize it at the time. Will this make my vaccine less effective? Should I get another one?

Illustration of a hand holding a positive COVID-19 rapid test over a calendar with 'Booster today' written on a crossed out date

Your experience is a good reminder that we all need to be alert to even mild symptoms, like the scratchy throat you had on the day you got your booster. Since the more transmissible Omicron variant has become dominant in the US, we’ve heard from a number of people who got a booster while unknowingly infected. Like you, they often had symptoms so mild that they were obvious only in retrospect. We’ve heard from others who got infected during the week following their booster, before the additional protection from that vaccine would have had a chance to kick in. Many of them are asking the same questions as you: Did my COVID-19 infection somehow “cancel out” the effects of my booster shot? Do I need to get boosted again?

Fortunately, the answer to both of those questions is “no.”

The CDC doesn’t recommend getting vaccinated while you are sick or after a known exposure, but this recommendation is intended to protect healthcare workers and others you might come into contact with while getting your shot. It’s also the case that being sick with COVID (or any other illness) at the time of your booster may exacerbate the normal side effects of the vaccine. In other words, if you were going to feel lousy after getting the shot, you’ll probably feel twice as crummy if you get it when you’re already infected with the virus. But the vaccine will still work as well as it otherwise would have.

No matter how you time it, that booster shot is going to do its thing — enlisting your cells to create harmless pieces of the spike protein found on the surface of the SARS-CoV-2 virus. This, in turn, will prompt your immune system to do its thing, churning out antibodies to respond to the perceived threat. But if you’re also infected with the actual virus at the same time, your immune system will be working overtime. Not only will it respond to the spike-protein impersonators generated by the vaccine; it will also be mounting a vigorous response to the virus itself.

This leads to the creation of even more antibodies, including the specialized antibodies that are the first line of defense against pathogens in the nose and upper respiratory tract — the entry point for the SARS-CoV-2 virus and the place the Omicron variant appears to multiply most rapidly. Mucosal immunity, the immune response generated in the moist tissues of the nose, mouth, throat, and lungs, depends on a different type of antibody (IgA) than that found in the rest of the body (IgG). We know that COVID-19 vaccination produces both types of antibodies, but we don’t know if vaccination-induced IgA antibodies have the same capacity for viral neutralization as those produced following natural infection.

Natural infection also leads to a broader antibody response in the rest of your body. With vaccination, your immune system learns to respond to the spike protein on the surface of the virus. But natural infection teaches the immune system to recognize and react to other parts of the virus as well, like the nucleocapsid protein, which is inside the virus and plays a critical role in allowing the virus to replicate once it has entered the body’s cells.

While there’s research suggesting that this type of “hybrid immunity” may be even more protective and longer lasting than the immunity produced by vaccination alone, it’s important to note that individual response to vaccination and infection varies from person to person. So, nobody should expose themselves to the virus intentionally in hopes of acquiring better immunity. And even though you’re unlikely to be reinfected with the Omicron variant, you shouldn’t drop your usual precautions against spreading or contracting the virus.

Bottom line? Don’t get another booster unless, or until, you are otherwise due for one, and don’t worry about not getting benefit from the booster you got. While everyone responds slightly differently to vaccination and infection, you should end up with at least the same amount of immunity you would have had after the booster alone, and possibly a little more.

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