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Is One Vaccine Dose Enough After COVID-19 Infection?

Posted on by Dr. Francis Collins

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.

  • Patrick D. Spurgin says:

    This blog post was back in February. Is there an updated analysis of the efficacy of 1 shot for persons previously infected?

    • Peg says:

      I have not seen any updates on this post, but more data is showing natural immunity after recovery is superior even to the shots. My husband still has high antibodies 18 mo after recovery and no shots. I still have antibodies after 1 shot obtained 8mo ago but I had antibodies before I got the shot. We don’t wear masks and have resumed a full social agenda including large concerts and stayed completely healthy and we are over 65! Hopefully when everyone stops posturing and playing political games we will get some truth but I’m not holding my breath.

  • Linda says:

    Haven’t seen anything related for a long time. I am wondering what advice there is for folks like me. I had Covid early in 2020. I was ill for 2 months. While my lungs eventually healed and bouts of tachycardia eventually subsided, I was left with weakness and discomfort of all sorts in my lower legs and feet. I got the two Pfizer vaccines and reacted badly to the first one (sick for a week) with horrible joint pains that continued past the second vaccine. The leg and foot problems got worse after the vaccines as did my tinnitus. Last summer the neurology work up determined I have Small Nerve Fiber neuropathy – idiopathic. I am at a loss as to what to do about the booster, terrified of getting so sick again. A recent antibody test showed antibodies of >800 detected. No one will advise me. All I keep hearing is “We just don’t know enough.”Anyone else in a similar situation?

    • Annie says:

      Hi Linda,

      My experience was similar to yours, including similar symptoms like heart palpiations, lower limb weirdness and extreme fatigue for months. Lost my sense of taste and smell for a couple of days. I had Covid in March 2020 that went into Long Covid. By fall of 2020, most of my Long Covid issues resolved Had first dose of Moderna vaccine in early March 2021. Didn’t really feel ill but experienced the heavy fatigue about a week after my first vaccine and continued to feel fatigue as well as “electric legs” and fibromyalgia symptoms up until the day before I was scheduled for the second dose. I finally felt good again and opted not to get the second dose at that time. Got a qualitative antibody test instead and levels were high. I still periodically experience the feeling in my lower legs as if electricity is running through them but it’s much better. I am considering the Moderna booster (because it’s a half dose) but am going to wait until they come out with a new mRNA in early 2022 that is supposed to address the variants like Omicron. Like you, I am very reluctant to take the chance of starting the cycle of Long Covid symptoms again. I also hope they will allow me to take the smaller dose booster, even though I never received the full second Moderna dose. Each Moderna dose was over 3 times the dose of a single Pfizer so with the combination of that significantly larger dose and having Covid, I feel protected. I still mask up in public places and avoid indoor gatherings unless everyone is vaccinated, I plan to avoid large, indoor gatherings this winter where people are unmasked and I don’t know the vaccination status of those attending. Hope this helps.

      • Linda says:

        Annie, thanks for sharing your experience and current thinking on boosters. My gut and my head are still arguing. So far my gut is winning out. I like the idea of waiting a bit to see what might be offered. I am also extremely cautious around others. All the best to you.

        • Annie says:

          Alan, thanks for sharing your experience. Like you, I did a lot of research (and agonizing) prior to deciding whether or not to get a second dose of Moderna one month after the first. My adult daughter was the only person who initially freaked out over my final decision to get a single dose of Moderna last spring and hold off for the second. Once I explained the rationale for my decision, she accepted it. Had I known then that a single dose of Moderna was over 3x a singke dose of Pfizer, my decision would have been easier. I am not opposed to a second dose or booster for myself, but plan to wait and see if Moderna tweaks their vaccine to address the Omicron variant.

    • ALAN ZAHN says:

      Hi Linda, I had a very severe case of Covid in March 2020. Hospitalized for two weeks and almost didn’t make it. I had my first Moderna vaccination around a year later (March 2021) and had a terrible reaction. High fever and the worst headache I’ve ever experienced. I knew my body was flooded with antibodies and I definitely didn’t want to take the second vaccination. I did a lot of research and found studies that supported my not needing a second vaccination. As we were having 25 people over for Thanksgiving, my wife was a little freaked out and asked me to get my second shot. I received my second full dose of Moderna and although I expected the worst, I had a much less severe reaction. Chills, 101 fever and general malaise for around 36 hours , but nowhere near as severe as my first reaction. FYI… I took an antibody test a week before my vaccination and the results came back greater than the highest measurement. Everybody Hass to follow their own path, but wishing you the best of luck!

      • Linda says:

        Alan, thanks for sharing your experience. I am glad your reaction was better than anticipated. This is so difficult.

  • Risa H Ehrlich says:

    Queries: (1) Can you have the current COVID variation and be SYMPTOM FREE?
    (2) If you have symptoms but test negative — what about the 3 day incubation period?
    ( 2) If you are symptom free, what difference should that make in your living situation ?
    (3) Can you have current Covid, test negative, be symptom -free and yet be infecting others?


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