CNN  — 

To get a booster or not? The US Food and Drug Administration and US Centers for Disease Control and Prevention have issued guidance that some adults can receive a third shot of the Pfizer/BioNTech Covid-19 vaccine, so it’s time to ask that question.

There are so many questions: Who exactly is eligible to get the booster? If you are eligible, should you rush to get inoculated? What should you consider in your decision-making process? And what about those who got the Moderna or Johnson & Johnson vaccines – can they get a booster too?

To sort through those questions, we spoke with CNN Medical Analyst Dr. Leana Wen. An emergency physician and professor of health policy and management at the George Washington University Milken Institute School of Public Health, she is also author of a new book, “Lifelines: A Doctor’s Journey in the Fight for Public Health.

CNN: A lot of people are confused about the latest guidance on boosters. Help us to break it down. Who is able to get a booster dose at this time?

Dr. Leana Wen: I think it’s important to clarify who is advised to get a booster versus who may get it.

In August, the FDA and CDC already announced that people who are moderately or severely immunocompromised and who received two doses of either the Pfizer or Moderna vaccines should get a third dose of the same vaccine. If you are in this category of people who received an organ transplant, are on chemotherapy for cancer, or have other immunosuppressing conditions, it’s advised that you get a booster dose now. (The FDA and CDC did not provide guidance for immunocompromised people who received the one-dose Johnson & Johnson vaccine.)

What was decided last week is for individuals who already received the two doses of the Pfizer vaccine, who are at least six months out from their second dose, and who are either 65 years old and above, or are 50 years old and above and have an underlying medical condition that makes them more likely to have a severe outcome from Covid-19. Those people are advised to get a third Pfizer dose, and should.

Shana Alesi administers a Covid-19 booster vaccine to Marine Corps veteran Bill Fatz at the Edward Hines Jr. VA Hospital on September 24 in Hines, Illinois.

Another, much broader group may get the Pfizer booster. That’s the group of adults ages 18 and above, who either have underlying medical conditions or who are in occupations that are high-risk for exposure to Covid-19. These individuals aren’t necessarily advised to get the booster but they may, once they weigh their own risks and benefits in consultation with their physicians.

CNN: Why make this distinction between “should” and “may”?

Wen: The thinking is that there is a group that’s the highest risk. That’s the people 65 and older, who reside in nursing homes, or who are 50 and over with underlying medical conditions. They should get the third dose and the data is clearest that they would benefit. The advisory panel essentially said that the benefit-risk calculation is a little less clear for those who are in the second, broader group. That’s why they may get the vaccine and can choose to get it, but it’s not yet advised that they do.

I think this is an important point. It’s clear those in the highest risk group should go out and get the third dose if they are past the six-month mark since their second shot. Then, there are others who should get to choose for themselves. We are at a point in the pandemic when people are making very different decisions about their own risks. I think it’s reasonable to let people decide about their own level of risk and whether they want a booster at this time.

CNN: What’s the difference between a third dose of the vaccine and a booster? People are using those words interchangeably.

Wen: They are interchangeable terms for the time being. Right now, someone in the US is considered “fully vaccinated” if they receive two doses of either the Pfizer or Moderna vaccines or one dose of the Johnson & Johnson vaccine. A “booster” is the term being used for another vaccine dose for someone who is fully vaccinated. For people who got the Pfizer or Moderna vaccines, which is the majority of the American public, that’s a third dose.

There are some experts who have said that this additional dose for those immunocompromised should not be considered a “booster” per se, as they never got the full immune protection to begin with from the first two doses. But that’s a very technical response. Practically, for those who got the Pfizer or Moderna vaccines, a “booster” and “third dose” mean the same thing.

CNN: What should people consider when deciding whether to get the booster?

Wen: Again, there is a group who really should receive the third dose – those advised by the CDC to do so. If you’re in this group, the booster very clearly has benefits in reducing your likelihood of contracting Covid-19 and of severe illness.

In the broader group who are allowed but not yet advised to get the booster, the evidence is clear that immunity to mild Covid-19 does wane over time. Protection still appears strong against severe infection. A third dose appears to increase protection against symptomatic disease.

Some people might look at that data and say, as long as I am protected against disease severe enough to lead me to be hospitalized, I don’t need a booster right now. Other people would say the opposite – they don’t want to get any Covid-19 at all. Something that’s considered mild could still be very uncomfortable to go through. That person may need to miss work or have child care concerns.

There could be long-term consequences to even a mild breakthrough infection. For a lot of people, avoiding hospitalization isn’t the only goal they care about. If you really want to avoid Covid-19, then that also could skew in favor of getting the booster once you hit your six-month mark.

Consider, also, your own health as well as risk exposures. The CDC has a list of underlying medical conditions that make it more likely that a person will have severe consequences as a result of Covid-19. These medical risks are additive. If you have, say, diabetes, heart disease, renal disease and emphysema, you are at higher risk of severe outcomes than if you have well-controlled diabetes alone.

Similarly, if you are mostly working from home, you may not have a lot of risk exposures, but if you are a teacher who is around a lot of unvaccinated and often unmasked kids in a cramped classroom, your risk is higher.

CNN: Are there any downsides to getting the booster?

Wen: The data from Israel, where there has been an extensive booster program, shows that the side effects from the third dose are comparable to those from the second dose. The most common side effects are local reactions like a sore arm and short-term symptoms like achiness, fatigue and chills that resolve within a couple of days.

The one concerning – though very rare – side effect is myocarditis, an inflammation of the heart muscle, which appears have the highest incidence among males of adolescent and young adult age. It’s important to note that the myocarditis associated with the mRNA vaccines is generally mild and resolves with no long-term harm – and that Covid-19 itself can cause myocarditis.

Still, especially if you are a younger male, but also if you are in the “may” versus “should” category, it is always a good idea to have a conversation with your doctor about the risks versus benefits of the vaccine.

CNN: What if you don’t technically meet the criteria for the booster? For example, what if your job doesn’t meet the CDC’s criteria for a high-risk occupation, but you’re going into work every day around unvaccinated, unmasked people?

Wen: To get a booster dose, all you need is a self-attestation. That means you get to make the decision. There is no doctor’s note or other proof of occupation or medical condition required. I believe that people should be allowed to make the decision for themselves, in consultation with their doctor, about what constitutes high risk. Going into a workplace where you’re surrounded by potentially unvaccinated people in an indoor, cramped setting certainly meets the common-sense test for what is high-risk.

CNN: Where should you go to get the booster?

Wen: The US government has set up an excellent “vaccine finder” website. You can look to see which local pharmacy or health clinic has the Pfizer vaccine and make an appointment that way. Also, check with your doctor – they may have the vaccine available too.

CNN: What about people who got the Moderna or Johnson & Johnson vaccines – can they get a Pfizer booster or a booster of Moderna or J&J?

Wen: Right now, the only people who got the Moderna vaccine who can get a third dose are those who are immunocompromised. Moderna and J&J are both submitting their booster doses for authorization by the FDA, and it should be a matter of weeks before we get more information. It’s not yet recommended to “mix and match” doses, so if you received Moderna, you should wait for the Moderna booster rather than getting the Pfizer booster.

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I know there’s a lot of talk of boosters now, but I want to make one thing very clear: The most important thing from a public health standpoint is still to make sure to people get their first doses of the vaccine.

Unvaccinated people make up the majority of people who are hospitalized and dying from Covid-19. They also constitute the majority of transmissions. Getting boosters for those vaccinated is an added plus to increase individual protection, and people should certainly do it if they so choose, but we also cannot lose sight of the importance of getting first doses into people who still remain unvaccinated.