Dr. Fauci Warns Not to Do This If You Got Pfizer

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The COVID-19 vaccines available in the U.S. have all been found to be highly effective. But as the Delta variant has quickly spread to become the dominant strain, breakthrough infections in fully vaccinated people have become more of a concern for some. But during a recent interview, Anthony Fauci, MD, chief White House COVID adviser, took time to warn people who got the Pfizer vaccine to not do one thing in the wake of a new study.

RELATED: If You Did This Before Your Pfizer Vaccine, You May Be More Protected.

While appearing on CBS' Face the Nation on August 15, Fauci was asked about a recent study that found the Moderna vaccine to be more effective against the surging Delta strain. When asked by host Nancy Cordes whether or not this meant anyone who originally got a Pfizer vaccine should seek out a Moderna booster shot when they become available, Fauci immediately pushed back.

"That study, first of all, is a preprint study, [and] it hasn't been fully peer-reviewed," he said. "I don't doubt what they're seeing, but there are a lot of confounding variables in there about when one was started, the relative amount of people in that cohort, that's Delta versus Alpha. We already implemented boosters for the immune-compromised. It's clear we want to make sure we get people, if possible, to get the boost from the original vaccine that they had."

The new research in question refers to a preprint study conducted by nfrence and the Mayo Clinic, which found that Pfizer's effectiveness dropped substantially against the Delta variant. The Aug. 8 study concluded that the vaccine was only 42 percent effective against the virus in July when Delta was the dominant variant, marking a significant drop in protection from the 95 percent efficacy recorded in clinical trials. On the other hand, researchers found that the effectiveness of Moderna against COVID infection dropped to 76 percent in July, down from 86 percent earlier in the year when Alpha was the most common version of the virus in the U.S.

RELATED: If You Got This Vaccine, Your Risk of COVID After Vaccination May Be Higher.

"Based on the data that we have so far, it is a combination of [two] factors," the study's lead author, Venky Soundararajan, PhD, told Axios last week. "The Moderna vaccine is likely—very likely—more effective than the Pfizer vaccine in areas where Delta is the dominant strain, and the Pfizer vaccine appears to have a lower durability of effectiveness."

But during the interview, Fauci also explained that there were some other differences between the vaccines that might explain the variation in levels of protection against the Delta variant. "Remember, the original dose of the Moderna is about three times what the dose of the Pfizer is," he said. "So you may have a difference in durability, but in general, the vaccines that have been approved for emergency use authorization and hopefully will be approved for a full authorization…are all really highly effective in preventing severe disease."

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Still, it may be some time before booster shots become available to the general public. During an interview on CBS This Morning on Aug. 12, Fauci admitted that while it was likely everyone will someday need a COVID-19 booster shot regardless of whether they originally received Pfizer or Moderna, officials would only be focusing on getting extra doses to the vulnerable parts of the population for the time being. "We don't feel at this particular point that, apart from the immune-compromised, we don't feel we need to give boosters right now," he said.

RELATED: Pfizer Only Works Against the Delta Variant If You Do This, New Study Says.