Moderna begins study of COVID-19 vaccine in children under 12

What we know about children and COVID-19 vaccines

When will children be able to get COVID-19 vaccines? It depends on the child's age, but some teenagers could be rolling up their sleeves soon.

CAMBRIDGE, Mass. - Moderna said Tuesday it has started a study of its COVID-19 vaccine in children under 12, including babies as young as 6 months.

The study aims to eventually enroll about 6,750 healthy children across the U.S. and Canada, the company said.

The announcement comes exactly a year after the first adult received a test dose of the Moderna shot, created at the National Institutes of Health. It’s now being used across the U.S. and in multiple other countries.

Moderna also has tested the vaccine in 12- to 17-year-olds but hasn’t yet released the findings. Researchers started with older children because they tend to respond to vaccines most similarly to adults.

The study in younger children will be more complex because scientists need to determine whether to use smaller doses than in adults and adolescents.

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FILE - Elementary school children take an exercise break outside at Rogers International School on Nov. 19, 2020 in Stamford, Connecticut. (Photo by John Moore/Getty Images)

Each child in the study will receive two doses of the vaccine spaced 28 days apart, as is done for adults currently receiving the shots.

Moderna said its study will be categorized into two parts. The first part will involve children between ages 2 to under 12 who will receive two doses of either 50 or 100 micrograms each. Children under 2 may receive two doses of either 25, 50 or 100 micrograms, the company said.

The first children inoculated will receive the lowest doses and monitored before later participants are given higher doses of the vaccine. An interim analysis will then be conducted to determine the best dose for each age group.

Part two of the study will involve children receiving the selected doses from the analysis — or placebo shots, the company said. Researchers will follow the participants for a year after the second vaccination to evaluate how well it works for younger children and the type of immune response it generates for them over time.

"It is humbling to know that 17.8 million adults in the U.S. have received the Moderna COVID-19 vaccine to date," said Moderna CEO Stéphane Bancel in a statement. "We are encouraged by the primary analysis of the Phase 3 COVE study of mRNA-1273 in adults ages 18 and above and this pediatric study will help us assess the potential safety and immunogenicity of our COVID-19 vaccine candidate in this important younger age population."

Children develop serious illness or die from COVID-19 at much lower rates than adults, but can still spread the virus — and infectious disease experts say immunizing this segment of the population is crucial.

"There’s no question: we do want to immunize children," said Drexel University pediatrics professor Dr. Sarah Long.

"It’s unlikely we could get community protection without immunizing children," Long added. "This is the lynchpin to getting everything back to some kind of normalcy."

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Moderna’s two-dose vaccine is one of three currently approved for use in the U.S. against COVID-19, given the green light by the Food and Drug Administration on Dec. 28. Two other shots, one by Pfizer-BioNTech and a single-dose vaccine by Johnson & Johnson, are helping to ramp up vaccine supply as the country works to stem the virus that has killed 535,000 Americans.

The Pfizer vaccine already is cleared for use starting at age 16, meaning some high schoolers can get in line for those shots whenever they become eligible in their area — either because of a medical condition or once availability opens up.

Pfizer has also completed enrollment for studies of children ages 12 and older and is expected to study younger children this year.

To date, the U.S. has administered more than 100 million doses of COVID-19 vaccine, averaging about 2.2 million vaccine doses administered per day. President Joe Biden has declared that states should open eligibility to all adults for coronavirus vaccinations by May 1.

Moderna also announced this week that it has dosed the first patients in an early-stage study of its "next-generation" shot. The new candidate, called mRNA-1283, could potentially be stored in refrigerators instead of freezers making it easier to distribute and administer — particularly in developing countries.

This story was reported from Cincinnati. The Associated Press contributed.