Moderna's Half-Dose Booster May Expand Global Vaccine Supply

Hands up if you got vaccinated

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Key Takeaways

  • Moderna is seeking FDA authorization for a third dose of its COVID-19 vaccine for the general public.
  • Data presented by the company indicates that a booster shot containing half the initial dosage is effective at creating a strong immune response.
  • If the half dose is authorized, Moderna could potentially ramp up its global vaccine supply.

Moderna submitted data to the Food and Drug Administration (FDA) last week for the evaluation of a third dose of its COVID-19 vaccine.

The company said that a 50-microgram dose—half of the initial dosage—is effective at boosting the immune response in previously vaccinated people.

The Biden administration, already criticized for its poor messaging and handling of its booster rollout, requested data on the 100-ug booster as well to compare long-term efficacies, Axios reported. 

Moderna’s booster study reported that adults aged 65 and above saw the greatest improvement in protection and that the half dose appears to be effective against all variants of concern. The findings have not yet been peer-reviewed.

If proved effective, the reduction in Moderna's booster dosage could significantly expand the global vaccine supply.

“It takes less antigen to trigger an existing immune response than it does to create one from scratch,” Richard Kennedy, PhD, professor of medicine at the Mayo Clinic and co-director of the Vaccine Research Clinic, tells Verywell. “What they try to do with most medicines, including vaccines, is find the smallest dose they can get away with and have the strongest response.”

In biology, he says, more isn’t always better. The goal of the vaccine is to introduce enough antigen—molecules that kick the immune system into gear—so that the body can create sufficient antibodies to fight an infection.

Loading the body with too much antigen, however, may lessen the competition from immune cells to produce the most specialized antibodies, potentially decreasing vaccine efficacy.

Although White House officials said that most Americans will need a booster shot eight months after their second dose, the rollout plan is not yet finalized. The FDA is scheduled to meet on September 17 to review the necessity of authorizing a third dose of Pfizer’s Comirnaty vaccine for the general population.

Anthony Fauci, chief medical advisor to President Biden, told CNN that Pfizer is on track to receive the go-ahead. But authorization for Moderna’s booster shot may be delayed for a week or two.

"We would have liked to have seen it happen all together, simultaneously. But ultimately the plan will be implemented, as was originally put forth," Fauci said.

The New York Times reported that top federal health officials urged for more time to review the clinical data and may limit boosters to only some recipients of the Pfizer vaccine.

It’s unclear if the health agencies will recommend people vaccinated with the Moderna vaccine to receive an additional shot from Pfizer. Preliminary studies indicate that mixing the two mRNA vaccines may be effective and possibly advantageous.

If authorized for a 50-ug booster shot, Moderna’s COVID-19 vaccine supply would double. This may benefit countries where vaccine supply is low, Kennedy says.

Doubling Moderna’s vaccine supply also means doubling the company’s potential revenue.

“On the company side, they come out and say ‘everyone needs a third dose.’ Is that because the data suggests it, or is that because the company would really like to sell third doses to hundreds of thousands of Americans?” Kennedy says.

While booster shots with reduced cost could be a financial gain for Moderna, Kenney adds, it will hopefully translate to lower vaccine cost for governments around the world as well.

What This Means For You

The White House has set the goal of rolling out booster shots starting the week of September 20. However, regulators have yet to sign off on third doses for the general population, and officials say Moderna and Johnson & Johnson boosters may be delayed.

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.

By Claire Bugos
Claire Bugos is a health and science reporter and writer and a 2020 National Association of Science Writers travel fellow.