What we know so far about the effort to vaccinate children

To achieve herd immunity, experts say kids need to get vaccinated, reducing the virus's ability to spread.

Millions of parents breathed a collective sigh of relief this week as the preliminary results of the Pfizer/BioNTech COVID-19 vaccine trial in 12 to 15 year-olds revealed what so many had been hoping for: The vaccine works in teens too.

“Jubilation—that was my response,” says Nia Heard-Garris, an attending pediatrician at Lurie Children’s in Chicago and assistant professor of pediatrics at Northwestern University Feinberg School of Medicine—and a parent herself. She wasn’t the only one feeling that way.

With nearly a third of the country having already received at least one dose of a COVID-19 vaccine and more than 2 million vaccinations occurring every day, the cloud of anxiety that has plagued the nation for the past year is finally beginning to lift. The end of the pandemic is in sight. Attaining herd immunity—the point at which transmission stops because the virus doesn’t have enough susceptible hosts to infect—now feels like a real possibility. But there’s a catch: The children must be vaccinated.

“We’ll never get to that population level of herd immunity until we vaccinate kids,” says Jennifer Nayak, division chief of pediatric infectious diseases at the University of Rochester Medical Center in New York. She was also “incredibly excited” by the Pfizer/BioNTech results.

“The fact that children are mounting a robust response to the vaccine is very positive and really bodes well that hopefully we’ll see the same thing as we move into the lower age groups in testing vaccines,” Nayak says.

With kids making up about 22 percent of the population in the United States, their immunity is crucial to reaching a national threshold of immunity, which experts estimate to range from 70 up to 90 percent, explains Tara C. Smith, an epidemiologist at Kent State University in Ohio.

Even if the U.S. reached that range without children, the disease would continue spreading because it’s herd immunity at the local, not national, level that matters, says Dominique Heinke, a postdoctoral researcher and epidemiologist in North Carolina. Even in a highly vaccinated population, unvaccinated people clustering together and interacting allows the virus to continue circulating, especially if they congregate indoors without masks and social distancing.

“That’s exactly what we see with kids’ social structures,” Heinke says. “Even if you’re at ‘herd immunity’ levels for adults, if the kids aren’t immune, either through natural immunity or through vaccination, then those chains of transmission aren’t getting broken and you’ve got a whole group of susceptible individuals where the virus can continue to transmit.”

The more transmission continues, the more the virus replicates and evolves, and the more opportunities it has to accrue mutations. “My biggest concern is the emergence of new variants,” Smith says. “We already have several here, and I’m concerned we’ll have more that could potentially escape immunity. I suspect we will see kids becoming a more prominent reservoir of this virus as more adults are protected by vaccination.”

Variants could keep the virus circulating

The variants that originated in South Africa (B.1.351) and Brazil (P.1), can infect people with immunity from previous infections, says Vaughn Cooper, a microbiologist and molecular geneticist at the University of Pittsburgh.

“That basically creates more chances for more infections in adults and more opportunities for transmission and subsequent evolution,” Cooper says. “To handle an evolutionary problem, you have to handle the number of evolutionary events. We’re not going to be able to stop that until we stop transmission among kids.”

Cooper also worries that the U.K. B.1.1.7 variant, which may be anywhere from 43 to 90 percent more contagious, and others like it will become the predominant viruses in the U.S. because they spread more easily. Since herd immunity is based on the reproduction number—the average number of infections that result from one infected person—a more contagious variant can also boost the level of herd immunity required to stop transmission, Smith says.

Unvaccinated and immune-compromised adults would therefore continue to be at risk for severe disease and death. And the risk is not zero for children either.

Kids left behind in vaccine trials

An estimated 3.4 million infections have occurred in children, according to the American Academy of Pediatrics, accounting for more than 13 percent of all U.S. cases. Children’s risk of death from COVID-19 is extraordinarily low—under 0.03 percent—and the most common complication, Multisystem Inflammatory Syndrome in Children is also rare, with just over 2,600 cases and 33 deaths through the end of February. But those numbers will increase as children make up an increasing proportion of infections.

Hence the frustration among some experts that it has taken so long to get pediatric vaccine trials running.

“What’s been hard from a pediatrician and a parent perspective is that we’ve been so excited about the COVID-19 vaccine and what this means for our lives, but really, we have left children out of that celebration and excitement,” Heard-Garris says, the attending pediatrician at Lurie Children’s in Chicago and assistant professor of pediatrics at Northwestern University Feinberg School of Medicine. “We’re a little late to the party. We should have thought about including kids from day one.”

In addition to their trial in adolescents, Pfizer is also testing their vaccine in 4,500 children ages 6 months to 11 years old. Moderna has an adolescent trial in progress and began recruiting  6,750 participants ages 6 months to 11 years old for another. AstraZeneca began a trial last month for those aged 6 to 17 years old, and Johnson & Johnson is planning a pediatric trial.

While there’s a good chance the FDA will authorize the Pfizer/BioNTech vaccine for that age group before school starts, results from the other trials aren’t likely until at least fall of 2021.

“What I’m worried about is that we are not going to roll these vaccines out fast enough to kids,” says Sallie Permar, chair of pediatrics at Weill Cornell Medicine and New York-Presbyterian Komansky Children’s Hospital. “We’re going to try to get them in their schools and their normal lives, which they need because we have a crisis on our hands in terms of mental health and obesity and all the things that came with social isolation and the shutdown. They may not be showing up with severe COVID disease, but they’re showing up with the symptoms of the social isolation in our health system.”

Weighing risks of social isolation against risk of disease

Returning to school before vaccines are available for all children means tough decisions for communities and families. Pediatric experts agree that returning to in-person school next fall must be a priority.

Joelle Simpson, interim division chief of emergency medicine at Children’s National in Washington, DC, says children need to be in classrooms next year whether or not they can get vaccines before school starts. She acknowledges how much researchers still don’t know about COVID-19 infections in children, including whether long-term effects are possible. But the evidence is clear regarding the negative impact on kids’ mental health, socialization, and development when they’re not in a school environment.

“We are certainly seeing an uptick in pretty severe mental health presentations as well as kids who have injuries from abuse, whether that be mental health or physical,” Simpsons says. “We have a school system that allows us to have trained eyes on kids to identify things like learning disorders, abuse and chronic conditions, which frankly cannot happen when they’re at home.”

Research has shown that wearing masks and maintaining three-feet distancing works well to prevent infections, Permar said. But questions remain regarding how well all schools can implement those measures and how officials will respond when infections occur.

“It would be amazing if every school had the resources they needed to be there five days a week and also offer virtual options for parents or caregivers that did not feel comfortable sending their kids back,” Heard-Garris says. “I don’t think that’ going to be a reality. If we see upticks in infection rates, then schools are going to go back the other way and kids will go back home, and that isolation and loneliness will get worse. If our children aren’t extended the vaccine or we don’t reach herd immunity, I worry those impacts are going to get bigger and bigger.”

Communities will need to strike a balance between the substantial benefits of in-person school and activities, and the risk of infection in that region and of individual populations, says Christopher Golden, an associate professor of pediatrics at Johns Hopkins University School of Medicine.

“We have not seen a spike in the number of kids that have had severe infections, but there are populations that may be at risk,” Golden says. “We’ve done a very important job of keeping people isolated and quarantined, but we still have seen that African American and Latino children and children with chronic medical conditions are at higher risk, so if we do open things back up again, there is the possibility that infections could increase and be more severe in at-risk populations.”

Inequities in vaccine distribution could worsen disparities

Even when pediatric vaccines do become available, disparities in some of these vulnerable populations may increase.

“It’s troubling,” Heard-Garris says, because many cities already are not equitably distributing vaccines to the racial and ethnic minority populations at highest risk. “One of the things we worry about when we talk about equity is that you can widen disparities inadvertently by offering certain interventions, such as offering a vaccine that a large population either can’t get or has concerns about.”

Experts also worry about vaccine hesitancy among parents, especially since no previous vaccine approved for kids older than toddlers has achieved coverage rates of more than 50 percent, Permar says. The longer it takes for vaccines to become available for children, the longer it will take to address that hesitancy and ultimately vaccinate enough children to make headway toward herd immunity.

“This virus isn’t going away, ever, but I think the pandemic, the mess that we’re in right now, it will have a very long and painful tail—many years—if we don’t vaccinate kids,” Cooper says.

So until widespread vaccination in kids returns them to normal classrooms, the rest of the country won’t be returning to true normal either.

“We’ll still have to have a lot of mitigation measures in place,” Heinke says. “It’s still going to be a matter of wearing masks, remaining distanced, probably limitations on the number of people in buildings and ventilation still being very important. To some extent, individuals will be able to live in a more normal existence if they’re vaccinated, but the whole society won’t be able to go back without vaccinating children.” 

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