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Research & Innovation, Family Health

Yale Begins Another COVID-19 Vaccine Trial in Children


Moderna studies are set to begin for ages 6 months to 12 years.

Note: Information in this article was accurate at the time of original publication. Because information about COVID-19 changes rapidly, we encourage you to visit the websites of the Centers for Disease Control & Prevention (CDC), World Health Organization (WHO), and your state and local government for the latest information.

For many reasons, we all urgently await proof that COVID-19 vaccines are safe for children. While the time frame for approved vaccines for kids—who make up roughly one-third of the U.S. population—is uncertain, studies are underway, and early results from a Pfizer-BioNTech trial for 12- to 15-year-olds are promising.

Since early in the pandemic, Yale has been conducting clinical trials for both adult and pediatric vaccines. This includes the above-mentioned Pfizer-BioNTech study of adolescents, and now, Yale is also participating in Moderna’s clinical trial for a vaccine for children 6 months to 12 years of age. 

Called KidCOVE, the Moderna phase 2/3 trial is being conducted at approximately 90 sites across the U.S. and Canada and will include 6,750 children. Inci Yildirim, MD, PhD, a Yale Medicine pediatric infectious disease specialist and a vaccinologist, is leading the trial at Yale. 

A rising concern

Developing a safe and effective vaccine for children has always been an important goal, but it is especially true now. Across parts of the country, including the Northeast and the Midwest, officials are reporting increases in COVID-19 cases among younger people, including children. Several factors, including the spread of more contagious variants and a full or partial return to normal activities, are believed to play a role. 

And there is also the threat of multisystem inflammatory syndrome in children (MIS-C), a rare but serious condition that appears to be linked to COVID-19 and which causes inflammation of multiple organs, often the heart. What’s more worrisome (and puzzling), is that many children and teenagers who have developed MIS-C, which can occur several weeks after contracting the coronavirus, did not have typical COVID-19 symptoms when they were infected. 

“As the pandemic has evolved, we have seen that kids really do get sick from COVID-19; they can get very sick and sometimes need invasive supportive care in the intensive care unit [ICU],” Dr. Yildirim says. “Any disease that brings our children to the ICU is important, and we need vaccines to bring them back to their normal lives.” 

I’m optimistic that kids today—seeing this pandemic happen—will see that the vaccines are safe and effective,

Inci Yildirim, MD, PhD, a Yale Medicine pediatric infectious disease specialist

Part of the problem, Dr. Yildirim says, is that so much remains unknown around COVID-19 transmission among kids. And after more than a year of social restrictions, it’s likely that many parents and kids have loosened up their guards, she adds. 

“When the pandemic first kicked in, we closed schools, we didn’t take our younger ones to grocery stores, and we didn’t do playdates—and we didn’t see kids getting sick as much,” she says. “Though we do not exactly know much about the role kids play in transmission of COVID-19, we do know that there are no other respiratory viral diseases in which they don’t play an active role—and we shouldn’t assume that COVID-19 is different. We have seen children transmitting SARS-CoV-2 [the virus that causes COVID-19] to other children and adults in summer camp or family gatherings. This is why we need vaccines for them. But in the meantime, we need to keep wearing masks, social distancing, and washing hands.” 

As for what is known as “long COVID,” or symptoms that linger for months after infection, Dr. Yildirim says it’s not clear how much this affects children as well. “However, we do see teenagers that, a month or two after an infection, maybe can’t run on the track as well as they did before, or if they are swimming, they can’t catch their breath. Basically, they are not really back to their ‘normal’ before the infection,” she says. 

A long road quickly shortened

Playing an active role in the development of vaccines for children has been rewarding, Dr. Yildirim says. And while much has been accomplished, there are still many questions to be answered.

“We have learned a lot since the pandemic started, but there are still many things we don’t know about COVID-19 and SARS-CoV-2 infection. But with the urgency of the pandemic, we used the skills and scientific discoveries we have been accumulating over the last decade or two to develop a vaccine in an incredibly short time,” she says. 

Dr. Yildirim was an investigator in the phase 1 Moderna vaccine trial that started in March 2020. “It was the first time a human being received that vaccine. And within nine months, I got the same vaccine in my arm,” she says. “Usually, from the lab to your arm, it takes 15 to 18 years to develop a vaccine. And with significant support from Operation Warp Speed, and the collaboration among scientists, clinicians, patients and, most importantly, our participants in the trials, we have been able to do this.”   

For this new phase of the trial, Dr. Yildirim says she has been pleasantly surprised at the hundreds of parents who applied to enroll their children. In fact, there is a waiting list. 

“This is the same vaccine that millions of adults and more than 1,500 children ages 12 to 17 years have received in a clinical trial, and the main purpose of this study is to test what is a safe and effective dose for this younger age group,” she says. “Kids are not little adults. As they grow, their immune system gets more mature and may respond differently to vaccines.” 

Because of these potential differences in responsivity, trial participants will be grouped by age: 6 months to 2 years old, 2 to 6 years, and 6 to 12 years. Each age group, starting with the oldest, will receive a low dose of the vaccine. Once that is proven to be safe, the dose will be increased to see how the children tolerate it and if it is effective. If the lower dose is equally safe and effective, that it is what will be used. 

For frame of reference, adult dosing for the Moderna vaccine is 100 micrograms, Dr. Yildirim says. For children, the dosing will start at 50 micrograms for the older kids and 25 micrograms for the youngest. 

Throughout the trial, multiple checkpoints examine the safety of the vaccine, with much closer monitoring than an adult clinical trial, Dr. Yildirim says. Another reason for the added precautions, she explains, is that children receive many routine vaccinations. This gets factored into scheduling the doses, to ensure the Moderna vaccine doesn’t interact negatively with other vaccines. 

“Kids are not little adults. As they grow, their immune system gets more mature and may respond differently to vaccines," says Inci Yildirim, MD, PhD, a Yale Medicine pediatric infectious disease specialist and a vaccinologist

Dr. Yildirim hopes that data paving the way to apply for authorization from the Food and Drug Administration (FDA) will be available by the end of the summer. If all goes according to plan, the vaccine could be available in early 2022.

In addition to bringing the pandemic to an end, Dr. Yildirim says she hopes the successes of the COVID-19 vaccines helps people become less hesitant about other vaccines. 

“When you are not aware of how bad an infection can be, your interest in getting a given vaccine may be different than it was 50 years ago when you regularly heard about people who were getting polio and chickenpox,” she notes. “I’m optimistic that kids today—seeing this pandemic happen—will see that the vaccines are safe and effective. They will hopefully appreciate that it is the most successful public health tool that is second to clean drinking water.“

While the work with vaccines continues, Dr. Yildirim says there is much that can be done to prevent infection until everyone—big and small—can be vaccinated. “Physical distancing and handwashing do work, and complying with mask rules is so important,” she says.

Additional reporting by Jeanna Lucci-Canapari.

[Visit Yale Medicine's Vaccine Content Center for more stories on COVID-19 vaccines.]

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