Don't Get a Moderna Booster Before Asking This, Experts Warn

No matter which vaccine you got first, make sure you know this before a Moderna shot.

More than 21 million people have already received their booster, with over 6 million choosing Moderna, according to the Centers for Disease Control and Prevention (CDC). Millions more are likely eligible for an additional shot, but might be waiting to book their appointment in order to decide which vaccine to get. Both the CDC and the U.S. Food and Drug Administration (FDA) have authorized mixing and matching booster doses, so eligible recipients of any of the three vaccines can choose which they would prefer to get for their next dose. And though health officials are largely abstaining from recommending one booster over the other, experts do have a warning for those getting the Moderna booster.

RELATED: Dr. Fauci Just Urged Vaccinated People Not to Do This.

Anyone eligible and six months out from their second Moderna or Pfizer shot or two months out from their Johnson & Johnson shot can get a Moderna booster. But when the FDA authorized Moderna's booster, they authorized a half dose of the manufacturer's original vaccine, instead of a full dose, as the agency did with Pfizer and Johnson & Johnson's boosters.

Rather than being a full 100-microgram shot, the Moderna booster is 50 micrograms. But your booster will still come from the same vials that full doses come in, so healthcare providers must make sure to draw out half as much for each shot, according to Stat News.

Virus experts say you should be making sure you get the half dose and not the full dose. "It has to do with the immune response that you have to Moderna. So, the data is showing that you don't need the full dose for that third dose," Kristi Durbin, the immunization program manager for El Paso County Health in Texas, explained to FOX21 News.

In terms of seeking out larger doses than have been authorized, David Hirschwerk, MD, an infectious diseases specialist at Northwell Health, told WebMD, "More is not better—you want the doses as recommended. If more were better, that is what the official recommendation would be."

RELATED: Dr. Fauci Says Doing This With Your Booster Creates More Antibodies.

This also applies to Johnson & Johnson recipients who might be seeking out a Moderna booster. According to early data from a National Institutes of Health (NIH) and the National Institute of Allergy and Infectious Diseases (NIAID) study, getting a Moderna booster after your Johnson & Johnson shot increases neutralizing antibody levels 76-fold within 15 days, while a Pfizer or Johnson & Johnson booster raise these levels 35-fold and 4-fold, respectively.

"If someone's gotten the J&J vaccine, I would get the half-dose Moderna, if that's the choice," Amesh Adalja, MD, a senior scholar at the Johns Hopkins University, told CBS-affiliate WUSA 9 in Washington D.C.

William Schaffner, MD, a professor of medicine in the Division of Infectious Diseases at Vanderbilt University added to the news outlet, "I don't think that the side effects will be that much greater if you've got the Moderna full-dose vaccine, it's just that's not the one that's currently recommended as a booster."

There is one group for which a full dose of Moderna is recommended for the third shot: those who are moderately to severely immunocompromised. The CDC authorized people in this group to get an additional shot of either Pfizer or Moderna, based on whichever vaccine they received initially, before authorizing boosters for anyone else.

"People with moderately to severely compromised immune systems are especially vulnerable to COVID-19, and may not build the same level of immunity to 2-dose vaccine series compared to people who are not immunocompromised," the CDC says. "This additional dose is intended to improve immunocompromised people's response to their initial vaccine series."

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Mixing up the correct dosage for Moderna boosters and third shots for immunocompromised individuals is not just a theoretical—it's already happened. On Nov. 5, the Mercer County Health Department in West Virginia had to temporarily halt COVID vaccine administration after the department erroneously gave full doses of the Moderna vaccine as booster shots, per WVNews.

"Our team is going to go in next week to make sure the vaccines can be given in the right doses," Ayne Amjad, MD, the state's health officer, told the news outlet. "This is not something that happens necessarily just in Mercer County, it's happened in other counties across the state."

During an earlier FDA committee meeting to vote on Moderna boosters, Jacqueline Miller, MD, Moderna's head of infectious diseases therapeutics, acknowledged that the different dose requirements "will require some education and enforcements," as reported by CNN. According to Miller, the manufacturer was preparing to send a "Dear Health Care Provider" letter explaining exactly how to administer each different dose.

"In addition, our fact sheet is going to contain detailed information and we have a 24-hour call center to support healthcare providers in their administration efforts," Miller assured.

RELATED: The FDA Is Investigating Reports of This Rare Moderna Side Effect.

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