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Is a Second COVID-19 Shot Necessary If You've Been Previously Infected?

Man receiving a vaccine wearing a mask.

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Key Takeaways

  • A study shows that people previously infected by COVID-19 who got vaccinated had a stronger immune response than people who hadn't contracted the virus. 
  • A COVID-19 vaccine dose after infection could serve as a booster shot for existing immunity. 
  • It’s still too early to tell whether one COVID-19 vaccine dose would be sufficient for people who were previously infected.

At least 40 million people in the U.S. have already been fully vaccinated against COVID-19. High levels of immunity (94 to 95%), for both the Pfizer and Moderna vaccines are reached two weeks after the second dose. However, a new study conducted by Mount Sinai reveals that a second dose may not be necessary for people previously infected by COVID-19. 

Ania Wajnberg, MD, co-author of the study and a physician at Mount Sinai in New York, shares that 109 individuals with and without previous COVID-19 were included in the study.

“We’ve been following a group of high-risk healthcare workers since last year," Wajnberg tells Verywell. "A percentage of them already had COVID-19 and we followed them prior to vaccines and after the second shot."

She quickly realized that the vast majority of participants who had previously experienced COVID-19 had a large immune response to the vaccine. The previously infected participants developed antibodies within a few days of the first dose of the vaccine at a rate that was 10 to 20 times higher than uninfected participants.

Once participants have been infected, they develop antibodies, Uzma Syed, DO, board-certified infectious disease specialist based in New York, tells Verywell. “When your body develops antibodies, your immune system gets revved up anytime it encounters a pathogen," Syed says. "The next time you get exposed, the immune system goes full swing fighting to prevent infection.”

Syed explains that the infection and antibodies produced after infection can serve as the prime immune response, leading researchers at Mount Sinai to question whether a second dose is necessary for these patients.

What This Means For You

If you've previously been infected with COVID-19, you should still get vaccinated. Experts aren't sure how long you'll be protected from COVID-19 after infection, so it's best to play it safe and receive the vaccine. However, if you were treated for the virus with monoclonal antibodies or convalescent plasma, the CDC recommends you wait 90 days before getting vaccinated. 

Reactions to the Vaccine

The study also investigated vaccine reactions after the first dose in a second group of 230 participants. Eighty-two of them had previously tested positive for COVID-19 whereas 148 had not.

Wajnberg says that because people who have had COVID-19 were introduced to the antigen, “their immune response is stronger than people who didn’t have COVID," Wajnberg says. "And so the first shot for them behaves more like a booster." In other words, their body was “primed.” This means that the immune cells learned to recognize the spike protein of the virus, allowing cells to better respond.

For study participants who were vaccinated after they got COVID-19, Wajnberg shares that they experienced stronger side effects compared to the group that didn’t contract COVID. “Nothing serious. Overall, the vaccine was very well tolerated,” Wajnberg says. Muscle aches, headaches, fatigue, low-grade fever were stronger in people who had COVID-19 after their first shot.

More Research Is Needed

While the study shows promising initial results, Wajnberg says that it’s still too early to tell whether a second vaccine may not be necessary.

“We’re not yet able to conclude that the first shot is sufficient,” Wajnberg says. “But looking at the antibody response, we wanted to point out that the first shot creates a very strong response.” 

Wajnberg hopes to continue the research and look at responses from both infected and uninfected people post-vaccination. 

With further research is underway, Wajnberg and her team hope to be able to inform future policies. If the approach translates into public health policy, it could expand already limited vaccine supply while controlling for vaccine reactions experienced by previously infected individuals, Wajnberg said in a press release.

As the research continues, Syed states that getting vaccinated is still the best protection. “All three vaccines have proven to be safe and effective and have in fact prevented severe infection, hospitalization, and death,” Syed says. “With a novel virus for which there is no cure, this is the strongest tool in our toolbox to beat this virus.”

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.

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  1. Centers for Disease Control and Prevention. COVID Data Tracker. Updated March 18, 2021.

  2. EurekAlert. Second shot of COVID-19 vaccine may not be necessary in previously infected individuals - Mount Sinai. Updated March 10, 2021.

  3. Krammer F, Srivastava K, Alshammary H, et al. Antibody responses in seropositive persons after a single dose of SARS-COV-2 mRNA vaccine. N Engl J Med. Published online March 10, 2021. doi:10.1056/NEJMc2101667