Moderna struggles to find 3,000 adolescent volunteers needed for COVID-19 vaccine trial

Not enough adolescents are signing up for Moderna's COVID-19 vaccine trial, a federal official said this week, potentially delaying vaccine authorization for this age group.

Last month, the U.S. Food and Drug Administration OK'd use of the Pfizer-BioNTech vaccine for 16- to 17-year-olds, as well as adults. The companies did not have enough data in younger adolescents to apply for use in that age group, and Moderna had tested its vaccine only in adults, so it is authorized only for those 18 and up.

About four weeks ago, Moderna launched a trial in 12- to 17-year-olds, but apparently, the company is struggling to find enough adolescent volunteers.

Moncef Slaoui, the scientific head of Operation Warp Speed, the government's vaccine effort, said Tuesday that while a vaccine trial in adults is accruing 800 volunteers per day, the teen trial is getting only about 800 per month.

The study needs at least 3,000 participants, he said, to provide valid safety and effectiveness data, and get authorization from the FDA.

"It's really very important for all of us, for all the population in America, to realize that we can't have that indication unless adolescents aged 12 to 18 decide to participate," Slaoui said.

COVID-19 has disrupted schooling, killed at least 172 US children

Although teens tend not to get very serious cases of COVID-19, they can get sick and they can pass on the virus that causes the disease. More than 2 million minors were diagnosed with COVID-19 in 2020, and many more probably contracted the disease but were never diagnosed.

This fall, U.S. counties with large colleges or universities that held in-person classes saw a 56% increase in COVID-19 cases after classes started, and college students fueled the 19 hottest outbreaks in the U.S. during the fall semester.

Children and teens may not bear much of the burden of the infection, but they are "bearing a disproportionate burden of the overall pandemic impact," said Dr. Lee Savio Beers, president of the American Academy of Pediatrics and a professor of pediatrics at Children's National Hospital. "We should not forget that."

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Children's schooling has been disrupted, along with their social lives and extracurriculars. Happening at a time when their brains are still growing and developing, "there is the potential for much longer-term impacts for them," than for adults, Beers said. "It really is a crisis situation."

While COVID-19 is generally mild in children, in rare cases, it can cause serious disease and even death. At least 172 American children had died of COVID-19 as of Dec. 17, compared with 166 who died of the flu during the 2019-2020 flu season.

Twelve-year-old Abhinav is one of the first children to join a COVID-19 vaccine trial. He got his shot on Oct. 22 at Cincinnati Children's, the same day as his father  Sharat also joined the trial.
Twelve-year-old Abhinav is one of the first children to join a COVID-19 vaccine trial. He got his shot on Oct. 22 at Cincinnati Children's, the same day as his father Sharat also joined the trial.

A spokesman for Pfizer said the company hopes to have data from 12- to 15-year-olds in the early part of this year and then, based on those findings, could start a trial in younger children in the spring.

For its part, Moderna said its trial is going just fine.

"While enrollment was lower over the holiday season, we expect to see an increase in the new year as planned," a spokesperson said via email. (More details on the trial are available here.) "We are on track to provide updated data around mid-year 2021."

Trial sites are limited at the moment, but will be expanding and people can preregister at

Vaccines tend to be tested in adults and then teens before being tried in younger children and babies, who may need lower doses or have different reactions.

Dr. Yvonne Maldonado, an infectious disease and global health expert at Stanford University School of Medicine, said it's crucial to get vaccine data for children of all ages.

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"Many of us want to see kids vaccinated – for their own safety of course, but also because it really reduces the chain of transmission," said Maldonado, chair of the committee on infectious diseases for the American Academy of Pediatrics.

But the fact that COVID-19 is usually so mild in minors makes it hard for parents to justify enrolling their kids in trials, she said.

"If the disease were something that was very clearly impacting them in a hugely negative way, you'd probably see more interest there," she said.

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Even if parents want their kids to participate, it may be tough to get a busy adolescent to participate in the two-shot process.

"It's a pretty recalcitrant group in general," noted Maldonado, the mother of three, now grown.

Children over age 7 are generally asked to agree to take part in a trial, even if their parent signs off on it.

Trial volunteers are given two shots of the vaccine 3-4 weeks apart and their blood is drawn several times.

Still, there are plenty of parents and teens who want to participate in vaccine trials, said Dr. Barbara Pahud, a pediatric infectious disease specialist and director of research for the Infectious Diseases Division at Children’s Mercy Hospital in Kansas City.

Pahud is not helping to run any pediatric trials yet, but she plans to, and expects many in her community and elsewhere will want to join as word of the trials gets out.

"A month from now, the situation might look very different," she said.

Pahud said she's not surprised that Moderna is taking longer to sign on teens than adults. Pediatric trials, she said, are simply used to a slower pace.

"There's no reason to expect them to enroll at the same rate" as adult trials, she said.

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The federal government and vaccine makers have not put as much emphasis on testing vaccines in children or pregnant women as it did in adults, Pahud said – not including either group in initial studies – and that needs to change if they want to pick up the pace.

Dr. Robert Frenck Jr., director of the Vaccine Research Center at Cincinnati Children’s Hospital Medical Center, said he's also not surprised that enrollment so far has been slow in Moderna's trial.

"Whenever you move into a new age group for a vaccine/drug, it takes a bit of time to build momentum," he said via email.

Timing also makes it harder to vaccinate minors, he said. While clinical trials are generally set to run during the workday, children are not available until after school hours, decreasing the time available to sign them up, he noted.

Frenck, who is helping to run the Pfizer trial in adolescents, said his pace was slow at first, too.

"But, as the teens enrolled, many told their friends about the study which significantly boosted enrollment," he said, adding that he expects that to happen with Moderna's trial, too.

If they can stick to current schedules, both vaccines may be available to adolescents before the start of the 2021-22 school year, though it remains unclear when they would be authorized for use in younger children.

Contact Karen Weintraub at

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This article originally appeared on USA TODAY: Moderna COVID-19 vaccine trial struggles to find adolescent volunteers