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Is One Vaccine Dose Enough After COVID-19 Infection?

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COVID-19 vaccination record card
Credit: iStock/Bill Oxford

For the millions of Americans now eligible to receive the Pfizer or Moderna COVID-19 vaccines, it’s recommended that everyone get two shots. The first dose of these mRNA vaccines trains the immune system to recognize and attack the spike protein on the surface of SARS-CoV-2, the virus that causes COVID-19. The second dose, administered a few weeks later, boosts antibody levels to afford even better protection. People who’ve recovered from COVID-19 also should definitely get vaccinated to maximize protection against possible re-infection. But, because they already have some natural immunity, would just one shot do the trick? Or do they still need two?

A small, NIH-supported study, published as a pre-print on medRxiv, offers some early data on this important question [1]. The findings show that immune response to the first vaccine dose in a person who’s already had COVID-19 is equal to, or in some cases better, than the response to the second dose in a person who hasn’t had COVID-19. While much more research is needed—and I am definitely not suggesting a change in the current recommendations right now—the results raise the possibility that one dose might be enough for someone who’s been infected with SARS-CoV-2 and already generated antibodies against the virus.

These findings come from a research team led by Florian Krammer and Viviana Simon, Icahn School of Medicine at Mount Sinai, New York. The researchers reasoned that for folks whose bodies have already produced antibodies following a COVID-19 infection, the first shot might act similarly to the second one in someone who hadn’t had the virus before. In fact, there was some anecdotal evidence suggesting that previously infected people were experiencing stronger evidence of an active immune response (sore arm, fever, chills, fatigue) than never-infected individuals after getting their first shots.

What did the antibodies show? To find out, the researchers enlisted the help of 109 people who’d received their first dose of mRNA vaccines made by either Pfizer or Moderna. They found that those who’d never been infected by SARS-CoV-2 developed antibodies at low levels within 9 to 12 days of receiving their first dose of vaccine.

But in 41 people who tested positive for SARS-CoV-2 antibodies prior to getting the first shot, the immune response looked strikingly different. They generated high levels of antibodies within just a few days of getting the vaccine. Compared across different time intervals, previously infected people had immune responses 10 to 20 times that observed in uninfected people. Following their second vaccine dose, it was roughly the same story. Antibody levels in those with a prior infection were about 10 times greater than the others.

Both vaccines were generally well tolerated. But, because their immune systems were already in high gear, people who were previously infected tended to have more symptoms following their first shot, such as pain and swelling at the injection site. They also were more likely to report other less common symptoms, including fatigue, fever, chills, headache, muscle aches, and joint pain.

Though sometimes it may not seem like it, COVID-19 and the mRNA vaccines are still relatively new. Researchers haven’t yet been able to study how long these vaccines confer immunity to the disease, which has now claimed the lives of more than 500,000 Americans. But these findings do suggest that a single dose of the Pfizer or Moderna vaccines can produce a rapid and strong immune response in people who’ve already recovered from COVID-19.

If other studies support these results, the U.S. Food and Drug Administration (FDA) might decide to consider whether one dose is enough for people who’ve had a prior COVID-19 infection. Such a policy is already under consideration in France and, if implemented, would help to extend vaccine supply and get more people vaccinated sooner. But any serious consideration of this option will require more data. It will also be up to the expert advisors at FDA and Centers for Disease Control and Prevention (CDC) to decide.

For now, the most important thing all of us can all do to get this terrible pandemic under control is to follow the 3 W’s—wear our masks, wash our hands, watch our distance from others—and roll up our sleeves for the vaccine as soon as it’s available to us.


[1] Robust spike antibody responses and increased reactogenicity in seropositive individuals after a single dose of SARS-CoV-2 mRNA vaccine. Krammer F et al. medRxiv. 2021 Feb 1.


COVID-19 Research (NIH)

Krammer Lab (Icahn School of Medicine at Mount Sinai, New York, NY)

Simon Lab (Icahn School of Medicine at Mount Sinai)

NIH Support: National Institute of Allergy and Infectious Diseases


  • Peggy J Lovell says:

    Both my husband and I had COVID in January 2021. We had high fevers 104+ for two weeks followed with a week of 103+ then I my fever dropped to 101+ my husband continued spiking high fevers for five weeks. He finally dropped below 101 but kept a fever for six weeks. I forced myself to get out of bed everyday. I made food for us, Gave over the counter meds, and we drank plenty of liquids. My husband could barely move and when we did get out of bed the coughing and loss of breath was the most scared I had ever been in my life. Seeing my husband pale and lifeless was horrifying.

    I now have high blood pressure resulting directly from having COVID. My husbands oxygen levels dropped in the mid 60s I took him to hospital pinned a note to him. They released him said he was too old (56). Second trip to hospital again unable to breath and oxygen in low 60s the hospital gave him oxygen for 6 hours and sent him home said he had had it too long to treat.

    Older folks on here might remember the 1968 flu pandemic, I had it when I was a child (10) and survived it. I was alive when it started . . . Neither of us wanted to get the vaccine. I was ‘retired’ from my career because of COVID. Still receiving my severance I am hounding by my employer to get vaccinated. The possibility of losing my pension because I am refusing to be vaccinated really pissed me off. I weighed my options and regrettably got the Pfzier shot August 16th. Ironically it is the same day my mother died in 1965.

    I immediately had numbness in my arm down to my fingers and the burning sensation followed. Five days after the swollen redness ‘sunburn looking arm’ had subsided except at the injection sight I had a bright red area hot to touch and painful. I had a terrible headache Tylenol wouldn’t touch. I slept 14 hours a day for 4 days. Eleven days have passed and I still have a lump the size of a soft ball but no redness I have numbness in the side where the injection was and it feels like something is inside my arm still. My sister had no side effects at all. I WILL NOT BE GETTING THE SECOND SHOT.

    I believe the natural immunity from having COVID for six weeks was enough to sustain me against any variant coming my way. I am keeping positive vibes the poison I had injected doesn’t cause anything long term or shorten my life. Given the amount of cholesterol and lipids in the ‘shot’ I will be very curious how my lipid panel is affected.

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