This Is What Experts Want You to Know About the Pfizer Booster

From eligibility to side effects, here's what you need to know

As the surge from the Delta variant continues to taper down and more time ticks by since vaccines became available in the U.S., more and more people are becoming eligible to receive a third dose of COVID vaccine. But depending on your current situation you may have some questions about the booster (specifically the one offered by Pfizer)—from eligibility requirements to what side effects you can expect. To help bring some clarity to these questions and others you may have about a third dose of the Pfizer-BioNTech vaccine, we gathered the latest insights from research studies, doctors, and expert organizations. Read on to discover what you need to know about the Pfizer booster.

RELATED: Half of People Who Got Pfizer Have Lower Antibodies—Here's Why.

1
You are eligible if you meet certain criteria.

A senior woman speaks to her doctor about her health. She looks at her doctor after she explained to her what she needs to be healthy. The doctor is holding a tablet.
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According to Johns Hopkins Medicine, you are eligible to receive the Pfizer booster if you received your second dose of the vaccine at least six months ago and meet at least one of the following criteria: You are age 65 or older, live in a long-term care facility, are age 18 or older and have an underlying medical condition that could put you at higher risk of severe COVID-19, or are age 18 or older and work in a location that puts you at high risk of exposure to COVID-19.

Underlying medical conditions include, but are not limited to, cancer, diabetes, stroke, heart disease, and obesity. For a full list of conditions, possible exceptions, and other information about your eligibility, consult your doctor or visit the Centers for Disease Control and Prevention (CDC) website.

2
The third shot is the same as the first two.

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You may be wondering how, if at all, the third dose is different from the first two you received. And the answer is, it isn't, according to Albert Shaw, MD, PhD, a Yale Medicine infectious diseases expert.

"The simplest answer is that it's just another dose of a vaccine you received," Shaw explains. "The concept is to prolong protective immunity, particularly if there is evidence that protection is waning after a period of time."

RELATED: If You Got Pfizer, This Is When Your Protection Plummets, New Research Says.

3
You should only get the Pfizer booster if your prior two vaccines were made by Pfizer.

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According to Yale Medicine, "so-called "mixing and matching" of vaccines has been used in Europe and other places, particularly ones where there have been supply issues. And there have even been studies that suggest this approach—one dose of AstraZeneca's vaccine (which is not available in the U.S.) and one dose of Pfizer's vaccine—potentially offers increased protection. However, in the U.S., the current public health recommendations are that people should stick with one type of vaccine for all doses.

4
You will likely experience a similar reaction to the third dose as the second dose.

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Everyone reacts differently to vaccinations—from mild symptoms to more severe feelings of sickness. The good news is that with the third dose of the Pfizer vaccine, you will have an idea of what to expect.

According to a recent CDC study, most people that received the Pfizer booster "reported local and systemic reactions were mild to moderate, transient, and most frequently reported the day after vaccination." In addition, the CDC found that "the patterns of adverse reactions observed after dose three of Pfizer-BioNTech were consistent with previously described reactions after receipt of dose two."

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5
The most common initial reaction is pain at the injection site.

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In addition to finding that most patients react similarly to a third dose of the Pfizer as they did to the second, the CDC also determined the most common side effects in general experienced by patients who received the booster.

In a recent report that analyzed more than 22,000 participants who completed a check-in survey after receiving a third vaccine dose between Aug. 12 and Sept. 19, the CDC found that pain at the injection site was the most common initial reaction to the shot, followed by swelling, redness, and itching.

6
The most common side effect is fatigue.

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From the same report, the CDC found that the most frequently experienced side effect of a third dose of Pfizer was fatigue, which 51 percent of survey respondents reported feeling. Other common reactions reported by the participants included headache (38.4 percent), muscle pain (36.3 percent), joint pain (23 percent), fever (22.2 percent), chills (17.5 percent), and nausea (13.6 percent).

RELATED: Pfizer Just Made Another Major Announcement About Its Vaccine.

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