How much protection you have against COVID after being vaccinated can depend on a lot of different things, from your age to certain underlying medical conditions to which vaccine you get. Of course, everyone wants the highest level of protection from their shots, especially as the Delta variant takes over and COVID cases continue to surge across the country after weeks of good news. And while you can’t go back in time if you’ve already been vaccinated, you may find peace of mind from the results of a new study, which found that some recipients of the Pfizer vaccine have even more protection against COVID, depending on one pre-vaccination factor.
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A group of researchers in Qatar analyzed 814,734 recipients of the Pfizer and Moderna vaccines using two national cohort studies to compare the effectiveness of the vaccines among those with and without a COVID infection prior to vaccination. The researchers looked at incidences of breakthrough infections among the recipients of each vaccine and compared the number among those who’d had COVID prior to vaccination and those who hadn’t. And what they found was that the recipients of the Pfizer vaccine who’d had COVID before their shots were much less likely to catch the virus again.
According to the findings—which were posted on medRxiv on July 26, but have not yet been peer reviewed—those who had gotten infected with COVID prior to getting the Pfizer vaccine were more protected against the virus, specifically the Alpha and Beta variants, which were dominant during the study period. The Pfizer vaccine reduced the rate of a COVID breakthrough infection among those who previously recovered from the virus by 85 percent, compared to Pfizer recipients without prior infection.
“Among those vaccinated with [Pfizer], protection against infection was further enhanced and infection incidence was further reduced by prior infection,” the researchers stated in the study.
However, there was no marked difference in the number of breakthrough cases among those who’d gotten the Moderna vaccine, whether they’d had the virus prior or not. “In contrast, those vaccinated with [Moderna] were as well protected as those who received the vaccine after a prior infection,” the researchers said.
The authors note that the breakthrough infection incidence rates for both vaccines were low, despite Qatar experiencing COVID surges between January and June 2021 due to the Alpha and Beta variants. The researchers say this shows that both vaccines are effective at protecting recipients who had COVID prior to vaccination and those who had not.
The results of the new study are similar to an April report funded by the National Institute of Health (NIH) in the U.S. that found that just a single dose of the Pfizer vaccine produced antibody levels among those who had recovered from a COVID infection similar to the levels found in people without prior infection after two doses of the vaccine.
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The authors of the Qatar story concluded that their findings “may have implications for the potential need of a booster vaccination.” But while some experts have considered delaying second shots for those who have already had COVID as a result of research like this, the Centers for Disease Control and Prevention (CDC) still recommends individuals get both shots in a two-dose series according to the standard timeline, even if they’ve previously had COVID.
“You should get a COVID-19 vaccine regardless of whether you already had COVID-19,” the CDC says. “That’s because experts do not yet know how long you are protected from getting sick again after recovering from COVID-19. Studies have shown that vaccination provides a strong boost in protection in people who have recovered from COVID-19.”
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