In a new study from Rush University, researchers found 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.
They found higher SARS-CoV-2 antibody levels in previously infected individuals after 1 dose of the Pfizer vaccine, compared with uninfected individuals after 2 doses.
What’s more, giving previously infected people a second dose of the Pfizer vaccine did little to boost their antibody levels further.
In the study, the team tested 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.
Before vaccination, the unit in blood samples for antibodies against SARS-CoV-2 in people who’d previously had COVID was about 621. After one dose of the Pfizer vaccine, that level soared to a much more protective level of 30,000 AU/mL.
Adding in the second dose of the vaccine only nudged that number up slightly higher, to about 37,000 AU/mL.
For people 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 team says 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 findings could be important to vaccine rollouts across the United States and globally.
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The study is published in JAMA Network Open. One author of the study is Dr. James Moy.
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