You got omicron. Should you still get a booster?

A medical worker administering a vaccine to a patient.
A medical worker administering a vaccine to a patient. (Image credit: Karl Tapales via Getty Images)

As omicron surges across the country, the coronavirus variant is infecting many people who have received their initial vaccine course — two doses of an mRNA vaccine (Pfizer or Moderna) or one dose of Johnson & Johnson — but who have not yet gotten their booster shot.

So if you've had omicron, should you get a booster, and if so, how long should you wait after the infection has passed?

The short answer is yes, you should still get a booster, but you may need to wait at least a few weeks to maximize the protective effect of the booster shot, one expert told Live Science.

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Timing your booster dose

But let's say you didn't get around to getting a booster, and then became infected with omicron,, or you are still recovering from omicron. Should you still get boosted?

In that case, the CDC recommends waiting to get a booster until symptoms resolve and you finish isolation. People who test positive but never show symptoms can get their booster as soon as they have completed their isolation period. (You can read the current guidelines on how long to isolate at the CDC website; the guidelines vary depending on your symptoms, vaccination status and job.)

Excluding hospitalized patients, COVID-19 infections take about 2 weeks to recover from, Dr. Sharon Nachman, chief of the Division of Pediatric Infectious Diseases at Stony Brook Children's Hospital in New York told Live Science. She says to wait at least two weeks for symptoms to resolve because breaking isolation could lead to other people getting infected. Additionally, because most people mount a good immune response to the vaccine, which might make them feel sick, getting the vaccine when you’re actively infected can worsen symptoms and place more stress on your body. 

"You want to be sure that you have the best response possible to the vaccine," said Dr. Erica N. Johnson, chair of the Infectious Disease Board for the American Board of Internal Medicine and an assistant professor of medicine at the Johns Hopkins University School of Medicine. "It's not that it's unsafe to administer an mRNA vaccine earlier than that. It's just that you want to be sure that you had the most effective response," Johnson said. 

Why omicron is different

Omicron is different from past "variants of concern"  because it can easily infect both those who were previously considered to be "fully vaccinated" and those who have been infected with earlier versions of the coronavirus.Omicron accomplishes this feat  because it carries a high number of mutations on the spike protein — a major target for the body's neutralizing antibodies, which prevent the coronavirus from entering cells. At least 15 of those mutations are on the virus’s receptor binding domain, or the spot on the spike protein where the virus locks onto and enters cells, according to a study published Jan. 4, 2021n the journal Cell

And in fact, recent data published in The New England Journal of Medicine show that these mutations do indeed make omicron better able to evade the immune system. The study showed that the effectiveness of the Pfizer-BioNTech vaccine against hospitalization plummeted from 93% to 70% against omicron compared to  Delta infections. 

Another reason for the reduced immune response against omicron is waning immunity. A December 2021 study from Israel, also published in The New England Journal of Medicine,  showed that vaccine effectiveness decreases six months after the second Pfizer-BioNTech dose, making vaccine immunity less protective against any coronavirus variant. 

Why boosting is important

All of this means it's important to get a booster to protect against omicron. One study published to the preprint database medRxiv but not yet peer-reviewed found that a two-dose mRNA vaccine regimen provided no protection against infection with omicron. But vaccine effectiveness increased to 37% one week after an mRNA booster, that research found. 

Boosters increase the immune response by helping antibodies better identify multiple parts of  the coronavirus. Recent research published in the journal Cell found that mRNA boosters stimulate the production of cross-reactive antibodies, or antibodies that bind well to both omicron and earlier strains of the coronavirus. No matter which vaccine you started with, it's important to get a booster once you're eligible, Johnson said. 

"People who've just had the primary series are still very much at risk for infection with omicron, though their infection might not be severe," Johnson told Live Science. "But for people that have received the booster dose, that seems to offer effective protection against omicron infection and certainly against more severe disease."

As of Jan. 11, the Centers for Disease Control and Prevention (CDC) recommends that in most cases, adults receive a booster at least 5 months after full vaccination. (There are some differences depending on your age, whether you initially received the J&J shot and whether you are immunocompromised.) Both mRNA vaccines are the preferred choice for boosters. (You can read more about the current recommendations on the CDC's COVID-19 booster shot page.)

Either way, being infected with omicron is not a good reason to avoid getting boosted, Johnson said.

"Vaccination with a booster dose is absolutely necessary to achieve the best protection possible," Johnson said.

Originally published on Live Science.

Jocelyn Solis-Moreira
Live Science contributor

Jocelyn is a New York-based science journalist whose work has appeared in Discover Magazine, Inverse and Verywell Health, among other publications. She holds a master's of Psychology with a concentration in behavioral neuroscience and a bachelor's of science in integrative neuroscience from Binghamton University. She has reported on several health and science topics ranging from coronavirus news to the latest findings in gut health.