If You Get a Pfizer Booster, Expect These Side Effects, New Study Says

A study of more than 4,500 people shows what you might see after getting your third dose of vaccine.

Study after study has found that currently available COVID-19 vaccines offer plenty of protection against the virus. But the arrival of multiple variants has had some health experts concerned that a follow-up dose may be needed to ensure the vaccines stay effective against the mutated strains. In the U.S., the Centers for Disease Control and Prevention (CDC) has held off on recommending a third shot, citing a lack of data on how effective the vaccines remain over time and how people might react to the extra dose. Now, new research has some initial insight into which side effects you might be able to expect after getting a booster shot from Pfizer specifically.

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The findings come from a study conducted in Israel, where people aged 60 and older have been offered access to a third dose of the vaccine since late July. When a survey of side effects was conducted of roughly 4,500 people who received a Pfizer booster from July 30 to August 1, 88 percent reported that they felt "similar or better" compared to how they felt after their second shot of the regimen.

The most common side effect was soreness in the arm or injection site, with 31 percent of respondents reporting it on the survey. Another 15 percent of respondents felt other side effects commonly reported after the first two doses, including muscle aches, fatigue, or fever, while .4 percent reported chest pains or shortness of breath following the booster.

According to Ran Balicer, chief innovation officer of Israeli healthcare provider Clalit Health Services that ran the study, the results are "initial and self-reported." But the data allows for an early comparison of immediate side effects, finding that "it turns out that in most cases they are similar or less in the booster."

"Although we do not yet have long-term research on the efficacy and safety of the third booster dose, for the personal risk management of any person aged 60 plus, these findings continue to point to the benefit of immunization now, along with careful behavior among adults and avoiding gathering in closed spaces," Balicer told Reuters.

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While long-term studies and information may still be missing when it comes to side effects, new data Pfizer shared on July 28 found that a booster shot of its vaccine could afford protection beyond what the standard two doses create. The data suggested that people aged 18 to 55 who get a third dose see their antibody levels against the Delta variant shoot up more than five-fold from what they were after the second dose. Meanwhile, people aged 65 to 85 saw an even more significant spike in antibodies after a third shot, giving them more than an 11-fold increase in antibodies compared to what they had following their second dose.

During an Aug. 8 interview on NBC's Meet the Press, Anthony Fauci, MD, chief White House COVID adviser, said that booster shots would likely soon be necessary to keep up the effectiveness of both mRNA vaccines that are currently available. "If you look at the data from Pfizer—[the efficacy rate] went down from the 90s down to around 84 after a few months," he explained. "The recent data for Moderna shows that it isn't really going down, but everyone assumes, and I think correctly, that sooner or later you're going to see an attenuation to the point where we're going to have to give an additional boost to people."

However, Fauci explained that officials still needed more data to make a decision. "As soon as they see that level of durability of protection goes down, then you will see the recommendation to vaccinate those individuals. But, he added, "the vaccines are still doing what you originally wanted them to do—to keep you out of the hospital [and] to prevent you from getting seriously ill."

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Zachary Mack
Zachary is a freelance writer covering beer, wine, food, spirits, and travel. Read more
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