My Patients Ask — Why get the COVID vaccine if you’ve already had COVID? (an update)

My friends at have posted a new answer to this question based upon the latest research:

A person who has had COVID very likely has some protection against re-infection, particularly from the strain of the virus they caught, but there are several good reasons why someone who has had COVID should get vaccinated:

    • Reinfection is possible: In a general population about 1 out of 1,000 COVID patients have gotten it again; among Marine recruits, this has been shown be as high as 10%.
    • Vaccines can generate stronger immune responses: People who had mild infections tend to have lower neutralizing antibody activity than people who have been vaccinated.
    • Immunity can wane over time: Antibody levels fall with time. Furthermore, 7 months after infection, 20% of people with previous COVID did not have memory B cells, which are needed to mount a new antibody response.
    • New strains of the virus continue to emerge: Vaccination — particularly the first dose of an mRNA vaccine (Pfizer and Moderna) — has been shown to increase neutralizing antibody titers to the original and new strains by 10 to 1,000-fold among people who had COVID months before. On the other hand, the ability of the natural infection to increase neutralizing antibody titers to new strains has been shown to vary significantly, with non-hospitalized (i.e., less severe) convalescent patients showing significantly lower binding titers compared to hospitalized patients and vaccine recipients.
    • The vaccines, particularly the mRNA vaccines, have been shown to be safe and effective so far. This is based on millions of doses. Just be aware that, after the first shot, people who have had COVID are more likely to have temporary side effects (such as fever, headache, chills, muscle or joint pain) than people who have not had COVID.


Vaccination of people previously infected with the original (Wuhan) strains may better protect them against variant strains. Blood collected from people at about 4 to 8 months after infection only weakly neutralized the original (Wuhan) strain. Furthermore, in only about half of people did it neutralize the B.1.351 (South African) strain. However, following a single dose of Pfizer or Moderna mRNA vaccine, neutralizing antibody titers against both strains increased 1,000-fold (Stamatatos, medRxiv — preprint). Similarly, research among 63 people who had been infected with SARS-CoV-2 within the previous 12 months found that getting at least the first dose of the Pfizer or Moderna mRNA vaccines resulted in neutralizing antibody titers against the B.1.1.7 (U.K.), B.1.351 (South African) and B.1.526 (New York) variants that were at least ten times higher than in people with a previous infection who had not been vaccinated (Wang, medRxiv 2021 — preprint).

Keep in mind that the rate of vaccine-related side effects — particularly systemic ones (e.g., fever, headache, chills, muscle or joint pain) — after the first dose of the Pfizer or Moderna vaccine appears to be greater for people previously infected with SARS-CoV-2 than for those who have not been infected. A study among 83 people previously infected (i.e., seropositive) and 148 people not previously infected (i.e., seronegative) found that systemic side effects occurred more often in people who were seropositive compared with those who were seronegative. Local side effects (e.g., pain, swelling, redness), however, were similar among the two groups (Krammer, medRxiv — preprint). According to the FDA, the safety profile of the J&J vaccine was similar between people previously infected and those who were uninfected (FDA, Janssen COVID-19 Vaccine Frequently Asked Questions 2021).

People previously infected with SARS-CoV-2 may have only a muted response to the second dose of the mRNA vaccines. Research among 13 people who were seropositive (average age 41) and 19 people who were seronegative (average age 39) found that antibody response was robust after the first and second dose of the Pfizer vaccine in people who were seronegative, but antibody response was robust after only the first dose and muted after the second dose in people who were seropositive. In fact, at one week after the second dose, people previously infected with SARS-CoV-2 had fewer antigen-specific antibody-secreting cells in circulation compared to after the first dose, suggesting a poorer antigen-specific immune response. Reasons for the muted response after the second dose in people previously infected was unclear, but the researchers postulated that optimal strategies for vaccination may differ for those previously infected compared with those who were not (Samanovic, MedRxiv — preprint).

In fact, other researchers have postulated that people previously infected with SARS-CoV-2 may require only one dose of mRNA vaccines, as antibody response to the first dose in seropositive people was shown to be similar to or greater than that in seronegative people after the second dose (Krammer, medRxiv — preprint). However, other research found that antibody response to the first dose of mRNA vaccines (Pfizer or Moderna) was high only for those who had experienced many COVID symptoms (5 on average) and were already antibody positive, and not for those who had experienced only mild symptoms, suggesting that two doses may be necessary even among people who were previously infected with SARS-CoV-2 (Demonbreun, medRxiv 2021 — preprint). Because the efficacy of a single dose in people previously infected with SARS-CoV-2 is still unknown, the CDC continues to recommend that two-dose vaccination series be offered to persons regardless of history of prior SARS-CoV-2 infection.

The CDC states that reinfection is uncommon for up to 90 days after the first infection, and research among healthcare workers found that those with a history of SARS-CoV-2 infection appeared to be protected from re-infection for about 5 to 6 months post-infection (Lumley, N Engl J Med 2020; Hall, medRxiv — preprint). People previously infected with COVID seem to develop persistent cellular immunity, as shown in one study in New York among people with a history of COVID (mainly mild) who showed highly functional memory T cell responses at 6 months after infection (Breton, bioRxiv 2021 — preprint). However, another study in Washington state among people with a history of mild COVID showed that while antibodies against the virus declined rapidly starting at four months after infection, levels of specific memory B cells in the bone marrow (which can produce antibodies against COVID upon re-exposure) could be detected in about 80% of the people at seven months after initial infection, suggesting that the remaining 20% may not have developed a strong immune response upon initial infection and therefore could still benefit from vaccination (Turner, Nature 2021).

Less than 66% of people who had experienced mild COVID-19 infections in the Netherlands were shown to have sufficient antibodies to neutralize variants such as B.1.351 (South African) and P.1 (Brazilian), although they had sufficient antibodies to neutralize B.1.1.7 (U.K.). In contrast, all but one person vaccinated with the Pfizer vaccine, and all people hospitalized with COVID-19 (i.e., those with severe infection), had sufficient antibodies to neutralize all three variants (Caniels, medRxiv 2021 — preprint).

Another study among people with detectable antibodies from previous infection showed that about 1 out of 1,000 became reinfected within a few months of initial infection (Abu-Raddad, medRxiv — preprint). The reinfection rate was much higher in a study of 3,076 U.S. Marine Corp recruits: 10% of those with a history of COVID became re-infected during basic training, but this was much lower than the 45% of those without previous infection who became infected (Letizia, Lancet Respir Med 2021).

However, for those who received monoclonal antibodies or convalescent plasma as a treatment for COVID-19 before receiving any vaccine, vaccination should be deferred for at least 90 days after passive antibody therapy as a precaution. Similarly, those who receive passive antibody therapy after the first vaccine dose but before the second dose should defer the second dose for at least 90 days after therapy. For those receiving antibody therapy unrelated to COVID-19 treatment, there is no recommended deferral period for COVID-19 vaccination.


This blog was accurate as of the day of posting. However, as the COVID-19 pandemic rapidly evolves and the scientific community’s understanding of the novel coronavirus and the COVID vaccine develops, the information above may have changed since it was last updated. While I aim to keep all of my blogs on COVID and the COVID vaccine up to date, please visit online resources provided by the CDC, WHO, and your local public health department to stay informed on the latest news.

© Copyright WLL, INC. 2021. This blog provides a wide variety of general health information only and is not intended to be a substitute for professional medical advice, diagnosis, or treatment from your regular physician. If you are concerned about your health, take what you learn from this blog and meet with your personal doctor to discuss your concerns.


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