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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


  • Susan Via says:

    I donated a kidney to my now 84 year old husband 4 years ago. He is doing great and received second Moderna dose two weeks ago. My second dose is today. I had fever, terrible chills and headache for two days after my first dose, he had nothing but a sore arm after both doses an dfatigue after second dose. Of course he is on immunosuppressants and we cannot find much information on the effectiveness of the vaccine on solid organ transplant recipients. What is the most current data for them? Any ongoing studies? He is a retired MD and would be happy to volunteer.

  • Maryann says:

    I’m a 74 year old woman who had a lobectomy last year for a non small cell tumor. My CT scans are now clear. I had the 1st Pfizer vaccine on Jan 22, 2021 and the 2nd on Feb 9, 2021. I have had 2 qualitative antibody tests this week and both were negative for antibodies. Has anyone else had this experience?

    • maryann says:

      I just received an answer to my own question. Apparently it is perfectly normal for vaccine receivers to get a negative antibody response because the protein that covid has is known as ‘N’ protein, whereas the protein that the vaccine carries is known as a ‘spike’ protein and therefore it doesn’t register an antibody response. So, briefly, it means that a negative antibody response on the antibody test that is given after two doses of vaccine is perfectly normal. YAY!

  • simone a. says:

    I had symptoms I thought were due to the flu (extremely painful body aches, chills, fatigue, some fever – not much- for a full week) then, when I got the Covid-19 vaccine two weeks later (on Feb 11) I had again the same symptoms and I also vomited…on the carpet, I couldn’t hold it. Which had never happened before. The symptoms lasted only 24 hours this time. My doctor insisted I have had the flue previously. I insisted to get an antibody test. The test revealed I had had Sars cov2. (I had the blood test on feb 25, the results today), Now I am not sure if I should have the second vaccine; I fear it would be too much for my immune system. I might take some tylenol before the second vaccine (March 11). It seems that doctors don’t know much about it. By the way I am a teacher, I teach in person … and I am 75 years old. Born on August, 24th, 1945.

  • simone amselli says:

    I have family living in Israel. As this country is closely monitoring the Covid vaccines, and started administering the vaccines well before we did, I contacted my family. The answer I just received was: the persons who had contracted the virus and had the first vaccines, have been asked to wait 90 days before the second one. One person in particular ( a member of my family) who had the second vaccine after the 90 days had a very small reaction then.

  • Herpezine says:

    It is an interesting approach to take and you would expect that natural immunity will give you.

  • Loulou F. says:

    After two doses of the Pfizer vaccine, my antibody test is negative. Do I have protection?

  • Diana J. says:

    I had my first shot of moderna Gad. I had side effects. I got a second one on feb 8th and on the second day I had a small fever and chills. days after I got a severe rash on Both arms neck back and chest then they fade away turn light brown and stay in my skin light freckles then it starts over again with the rash most every day two weeks ago I noticed two big lumps on top of my clavicle the left one is very very painful I went to my md he said he did t know much I asked him to draw a CBC to see if I had an infection from it because I had heard of a doc getting the shots with the same thing I have and passed away 14 days later of brain bleeding I’m very scarred also my pulse has been very fast that I’m taking motropolol ans it does not even help it feels like I’m having a heart attack my heart pounds very fast can anyone please help me please?

  • Amy Cartwright says:

    Very specific and informative! Thanks for sharing this helpful content! Regards

  • Shirley J. says:

    Question. Should you get the second vaccine if you contracted Covid infection one day after first dpshot. Exposed at work. Not from shot

  • Ken Cole says:

    I caught something severe at a large meeting in San Francisco (30,000+ from all over the globe including China) the week of December 14, 2019. It resulted in a week in bed with severe fatigue and a persistent cough. The fatigue gradually subsided over the next couple of months while the cough persisted for 6-8 months.

    After my first Dose of Moderna Vaccine on Feb 15, 2021, I developed severe muscle spasms and cramps on day 3 – 6 along with fatigue. The fatigue subsided after 16 days. Now I am afraid of getting the second shot as it likely will produce an even stronger reaction.

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