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Ask the Expert: COVID-19 vaccine boosters

Sep 2, 2021

Editor’s note: This story was updated on Sept. 29, 2021, to include new and updated information on the recommendations from the Centers for Disease Control and Prevention as it relates to booster doses of a COVID-19 vaccine.

Half of Hoosiers are now fully vaccinated against COVID-19. While there are still millions of people who need their first dose of a COVID-19 vaccine, scientists are now researching the need for booster doses for those who have been fully vaccinated.

Dr. Lana Dbeibo, an expert in infectious diseases, a faculty member at the IU School of Medicine and one of the medical experts leading IU’s response to the COVID-19 pandemic, answers some key questions about booster doses of COVID-19 vaccines.

Question: What are booster doses for the COVID-19 vaccine?

Answer: A booster dose for any vaccine is an additional dose of the original vaccine after a certain amount of time when research has shown that the original immunity and protection begins to wane. For example, kids get boosters of several vaccines, including the MMR (measles-mumps-rubella) and chickenpox vaccines, during the typical childhood immunization schedule.

In the case of COVID-19, research is showing that after about six to eight months, the effectiveness of the mRNA vaccines (Pfizer and Moderna) is not as high as it is right after the initial two doses for mild disease. Effectiveness is still extremely high, however, and these vaccines, even without a booster, continue to protect people from severe disease and hospitalization.

Q: What’s the difference between a third dose and a booster dose?

A: Currently, the FDA has authorized a third dose of the mRNA vaccines for individuals who are severely immunocompromised, including those currently in cancer treatment or who have had an organ transplant. For those in this category, the third dose can be given 28 days after the second dose. This becomes part of the vaccine series for this group, who is at much higher risk from complications of COVID-19.

While it’s the same vaccine and same dosage, for the general population, this additional dose would be a booster given at least six to eight months after the initial two doses. We expect the FDA and CDC to announce further recommendations for boosters in the coming weeks.

Q: What are the current recommendations for booster doses?

A: On Sept. 24, the CDC announced its recommendation for a booster dose of the Pfizer vaccine for certain groups of individuals. These recommendations are for Pfizer only as data is still being reviewed and studied for the Moderna vaccine.

The CDC says the following individuals are eligible to get a booster dose at least six months after their second dose:

Q: If we need boosters, does this mean the vaccines don’t work?

A: Absolutely not. These mRNA vaccines are truly wonderful. We’re seeing them save countless lives and protecting people from severe disease. Getting a COVID-19 vaccine continues to be our best defense against the ongoing pandemic.

Many vaccines begin to lose effectiveness over time. It’s why boosters exist in the first place. They allow us to “boost” your protection against a particular virus.

Q: When should I get a booster?

A: I know a lot of people are anxious to get a booster, but honestly, I’m most concerned about anyone who has not had any doses of a vaccine getting fully vaccinated first. We know that that population continues to be most at risk for severe cases of COVID-19 and death from the virus. We’re seeing this over and over in our local hospitals, where the vast majority, if not all, of our hospitalized patients with COVID-19 in the ICU or on a ventilator are those who have not been vaccinated.

Q: I got the Johnson & Johnson vaccine. Can I get a booster?

A: Not yet. Research continues into booster or additional doses of the Johnson & Johnson vaccine. Right now, only the mRNA vaccines (Pfizer and Moderna) are being authorized for third doses in specific populations, and Pfizer is only authorized for booster doses.

Q: Will adding boosters have any effect on availability of the vaccine for kids when they become eligible or for those who are unvaccinated?

A: We’re lucky in the U.S. that we have ample access to the COVID-19 vaccines at this point. There are vaccine sites all across the state of Indiana, and we continue to work toward getting more and more people vaccinated.

We continue to wait for FDA guidance and authorization on giving a COVID-19 vaccine to those under 12 at this point.

Q: If I’ve not gotten any doses yet, can I just add on a booster after the first two?

A: Getting the first two doses of a COVID-19 vaccine is the most important step you can take at this point. Walk in to a vaccine site or schedule your appointment now. I can’t underscore how important vaccination is at this point in the pandemic, especially with the delta variant running throughout our communities. There is no reason to wait.

Once you have the first two doses and are fully vaccinated, you would then wait the recommended amount of time to get a booster as needed.

Learn more

For more information on the COVID-19 vaccines, you can view frequently asked questions on or review a special vaccine edition of Ask Aaron featuring Dbeibo and Dr. Aaron Carroll, IU’s chief health officer.


IU Newsroom

Amanda Roach

Executive Director of Media Relations & Editorial Content

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