One dose of Pfizer vaccine it’s enough for Individuals with a prior COVID-19 infection

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I think I’ve had COVID-19 already, so do I really need two doses of vaccine?

It’s a question millions of people around the world are asking, and now a small, new study finds that people who know they were infected with SARS-CoV-2 in the past may need only one shot of the Pfizer vaccine to gain strong immunity.

In fact, “we observed higher SARS-CoV-2 antibody levels in previously infected individuals after 1 dose of [the Pfizer vaccine], compared with infection-naive individuals after 2 doses,” concluded a team led by Dr. James Moy, of the division of allergy and immunology at Rush University Medical Center in Chicago.

What’s more, giving previously infected people a second dose of the Pfizer vaccine did little to boost their antibody levels further, “suggesting that 1 dose may be acceptable in this group,” the researchers added.

The bottom line: “Individuals with a documented prior COVID-19 infection may be sufficiently protected from reinfection after a single mRNA vaccine dose, which could free up availability of millions of additional doses,” Moy’s group reported.

The new study was small—29 Chicago-area residents with a prior case of COVID-19 infection based on PCR testing, and another group of 30 people with no such histories.

Participants averaged 42 years of age, and about three-quarters were women.

The study highlighted that prior infection alone is not a robust defense against COVID-19: At baseline, the arbitrary units-per-milliliter (AU/mL) in blood samples for antibodies against SARS-CoV-2 in people who’d previously encountered the virus was about 621. After one dose of the Pfizer vaccine, that level soared to a much more protective level of 30,000 AU/mL, Moy’s team reported.

Adding in a second dose of vaccine only nudged that number up slightly higher, to about 37,000 AU/mL.

For folks who had never encountered SARS-CoV-2 before, two vaccine doses were definitely needed to reach a good level of protective antibodies. After one dose, this group’s antibodies averaged just over 1,800 AU/mL in blood samples, but after getting a second dose that number jumped to more than 15,000 AU/mL, the research team said.

So, while two doses of the Pfizer vaccine are essential if you’ve never had COVID-19, one dose may be enough if you’ve already had it, the team concluded.

One expert in infectious disease said the findings could be important to vaccine rollouts across the United States and globally.

“Some proportion of the vaccine-hesitant are those who have had prior infection who are confused as to why they would be treated exactly as somebody without any prior immunity,” explained Dr. Amesh Adalja, who wasn’t involved in the new research.

The new data “should be used by [the U.S. Centers for Disease Control and Prevention] to update recommendations for those who have had prior infection, allowing them to need just one dose [of the two-dose vaccines] to be considered fully vaccinated,” said Adalja, who is senior scholar at the Johns Hopkins Center for Health Security, in Baltimore.

“This could increase the number of people vaccinated and remove a talking point of the anti-vaccine groups, who say that prior natural immunity is being ignored,” he added.


We found that COVID-19 recovered individuals develop a level of provoked antibody response, following a single dose of mRNA vaccine, that is comparable to the provoked antibody response seen after a two-dose vaccination course administered to infection naïve persons. Extending from similar results seen in smaller studies,5,6 our findings in a large and diverse cohort of healthcare workers highlight the potential of a strategy for maximizing vaccine supply that warrants further investigation.

Recent work has demonstrated that COVID-19 specific antibodies are efficiently generated and detectable in the circulation following a single dose of vaccines that were originally intended for complete administration to include an additional booster dose.5 These findings have prompted some organizations to favor prioritizing at least a first vaccine dose to majority segments of the population while considering variable timing for the second dose.

In the absence of clinical outcomes data to support any variations from pre-specified vaccination protocols,8–10 there are immuno-biological data suggesting possible alternate strategies for COVID-19 recovered individuals. In fact, detectable presence of naturally acquired anti-SARS-CoV-2 antibodies and measures of discernible T-cell mediated immunity, especially in persons who have successfully recovered from recent versus remote infection, have prompted some experts to suggest delaying any vaccination for these individuals.11–13

However, acknowledging the unclear duration of naturally acquired immunity and the unknown extent to which immunity to one strain of SARS-CoV-2 confers protection from variants, there is general agreement that vaccination strategies for COVID-19 recovered persons warrants careful consideration.

Our data suggest the potential benefit of at least one vaccine dose, given that we observed pre-vaccine levels of anti-S IgG in COVID-19 recovered persons to be somewhat lower than levels detected among infection naïve persons following a single vaccine dose. In the absence of directly measured neutralizing antibody levels, we secondarily examined the proportion of anti-S IgG values known to correspond with high titers of the PRNT assay and found a comparable albeit slightly lower frequency in COVID-19 recovered persons after a single vaccine dose compared to infection naïve persons after two doses.

Notwithstanding the need for further studies with additional serologic phenotyping, this finding may be related to heterogeneity within the COVID-19 recovered persons including variations in timing and severity of prior illness. Although circulating antibody levels alone are not definitive measures of immune status, serial measures of the serological response to either natural or inoculated exposures are known to correlate well with effective immunity14 and our results indicate their potential utility in guiding vaccine deployment strategies for both infection recovered and naïve persons.

Several limitations of our study merit consideration. We examined antibody response within 7 to 21 days following each vaccine dose, and longer-term follow up is likely to provide additionally informative data – particular regarding the putative duration of immunity acquired from receiving a single versus double dose of vaccine administration.

Direct measures of neutralizing antibody levels are a part of our ongoing work. Notwithstanding the size of our study cohort, yet larger-sized samples are needed for sufficient statistical power to examine differences across demographic and clinical subgroups that are known to exhibit variation in antibody response following vaccination.15–17

In summary, we found in diverse cohort of mRNA vaccine recipients that anti-S IgG levels are similar between those with and without prior COVID-19 infection after receiving their first and second doses, respectively. These results offer preliminary evidence in support of a middle ground between public health motivated and immunologically supported vaccine strategies.

If validated, an approach that involves providing a single dose of vaccine to persons with a confirmed history of COVID-19 infection along with an on-time complete vaccine schedule for infection naïve persons could assist with maximizing the benefit of a limited vaccine supply.

reference link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7924304/


More information: Find out more about the safety and benefits of COVID-19 vaccination at the U.S. Centers for Disease Control and Prevention.
Mark Anderson et al, SARS-CoV-2 Antibody Responses in Infection-Naive or Previously Infected Individuals After 1 and 2 Doses of the BNT162b2 Vaccine, JAMA Network Open (2021). DOI: 10.1001/jamanetworkopen.2021.19741 , jamanetwork.com/journals/jaman … /fullarticle/2782762

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