What's the Difference Between a Covid Vaccine Booster and a Third Dose?

Covid-19 booster vaccines are different from a third mRNA shot. The latter is now being administered to the immunocompromised.

By Allison Forsyth August 24, 2021

On Thursday, Aug. 12, the FDA amended the emergency use authorization for the Pfizer and Moderna Covid-19 vaccines to include a third dose of the vaccine, which is now available to certain immunocompromised individuals.

Third doses, however, are different from the booster shots the FDA is hoping to push through for emergency use authorization by September. Boosters will be available to all eligible vaccinated individuals.

Dr. Manuel Gordillo, infectious disease specialist at Sarasota Memorial Hospital, recently answered questions about third shots and booster vaccines.

Who is currently eligible for a third shot?

"The CDC and FDA are a little careful with their terminology. The third dose is approved for moderately to severely immunocompromised people. These people include those with cancer undergoing chemotherapy, transplant patients, people with AIDS, end-stage renal disease on hemodialysis, patients with no spleen, and more. There are also those with a variety of autoimmune diseases or those who take the medication Prednisone in moderate to high doses—more than 20 mg.

"The immunocompromised make up about 3 percent of the U.S. population, and they can go and get a third dose now."

How long should immunocompromised people wait to get the third shot?

"Suggested wait time between the first series and the third shot is 28 days or more. However, if 20 days have elapsed since your second dose of Pfizer or Moderna vaccine, you can get it."

Important: A booster is different than a third dose.

"Over time, the amount of antibodies to fight the virus decreases in the body, even if you've been vaccinated. Previously, the Moderna and Pfizer vaccines were providing 93 to 94 percent protection from Covid-19, but now that's down to about 80 percent, partly because of the variants. This means boosters may be necessary.

"Starting around Sept. 20, a booster mRNA vaccine for all eligible individuals should be in place. It will still have to go through the regulatory process; the FDA and CDC need to look at all the data and give the OK by mid-September. By then, I expect that some of us will need boosters, namely the elderly, health care workers and those living in nursing homes."

Will there be a Johnson & Johnson booster vaccine?

"The FDA and CDC are looking at Johnson & Johnson as we speak. The Johnson & Johnson vaccine was approved two months later than the mRNA vaccines. It's a younger vaccine and the FDA and CDC need more data before they give it approval for a second dose. Plus, the sheer number of J&J vaccinations is less than Pfizer and Moderna. For every 10 vaccines, nine are mRNA and only one is J&J.

"Those who are immunocompromised and wish to get a third shot right now are able to get Moderna or Pfizer. It is recommended to get the same brand shot the third time, but if you can't get, doctors may recommend the alternate."

In addition to the information provided by Gordillo, the Sarasota County Department of Health also has a comprehensive list of who qualifies for a third shot.

Eligible immunocompromised patients are those who have been receiving active cancer treatment for tumors or cancers of the blood; received an organ transplant and are taking medicine to suppress the immune system; received a stem cell transplant within the last 2 years or are taking medicine to suppress the immune system; have moderate to severe primary immunodeficiency (such as DiGeorge syndrome, Wiskott-Aldrich syndrome); have advanced or untreated HIV infection; and are undergoing active treatment with high-dose corticosteroids or other drugs that may suppress your immune response."

"The Centers for Disease Control and Prevention does not recommend additional doses for any other individuals at this time," the DOH's public health information officer, Steve Huard, adds.

For vaccine clinic information in Sarasota and Manatee County, as well as where to get a Covid test and how to apply for Covid-related assistance, click here.

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