When will teens and kids be able to get the Covid-19 vaccines?

With the news Wednesday from Pfizer/BioNTech that preliminary data suggests their vaccine is effective and safe in youth ages 12 to 15, Covid-19 shots for those under 16 seem like they might finally be on the horizon. But the big question of whether most kids will be able to get vaccinated before they head back to school in the fall remains.

Children were left out of the earliest vaccine trials as pharmaceutical companies prioritized adults at higher risk of hospitalization and death. Which made sense: The disease has killed approximately 270 children in the US, compared with more than 424,000 people age 65 and older.

But many kids have caught the virus, with about 3.4 million pediatric Covid-19 cases reported as of March 25 — likely a substantial undercount because these cases are often mild or asymptomatic. There have also been more than 2,600 children in the US who have gotten a severe inflammatory syndrome following infection, and many reports of children with persistent, debilitating symptoms after even a mild Covid-19 illness.

Not to mention the broader impact of the pandemic on children’s lives, with less social contact with peers and extended family members, increased risk of abuse at home, and major disruptions to education that is widening the existing chasms of inequality.

Because of these hardships, the National Academy of Medicine, in its fall 2020 recommendations for vaccine allocation, said that children should be in phase 3 of recipients — which would fall before the general adult population and in the same group as many essential workers. But this clearly did not come to pass.

Importantly, we have yet to formally ensure the vaccines are effective and safe in children, whose immune systems can work slightly differently than adults’. (Pfizer/BioNTech’s new data is preliminary and has not yet been peer-reviewed.)

But vaccine companies are racing to gather more data, and the FDA has okayed Pfizer and Moderna to start new studies of their vaccines in kids 11 and younger. Moderna has a trial underway and expects initial results in the coming months. Johnson & Johnson is still in the planning phases.

Pfizer/BioNTech say they’ll submit their new findings on adolescents to the US Food and Drug Administration in the weeks ahead in hopes of having their vaccine authorized for ages 12 and up. (It is currently authorized for emergency use for those 16 and older; Moderna and Johnson & Johnson’s vaccine can be given to those 18 and up.)

Here’s where we are in learning about the Covid-19 vaccines in children and teens — and what parents, teachers, and family members should do to keep the virus in check before they are ready.

Why most kids can’t get vaccinated for Covid-19 yet

The prospects for kids getting vaccinated are looking good. In addition to the new early Pfizer information on kids 12 to 15, we also have that reassuring pile of data about the vaccines’ safety and efficacy in adults. Nevertheless, several factors make these vaccine trials in children slightly more challenging.

“Since the infection is a mild one in the majority of children, the bar for a Covid-19 vaccine to be safe in children is even higher,” Kristin Moffitt, a pediatric infectious disease specialist at Boston Children’s Hospital, wrote in an email to Vox. “This is different than an experimental medication designed to treat a terrible disease, where side effects might be tolerated. A vaccine designed to prevent infection must be safe.”

We also cannot assume the vaccines will behave in children exactly as they do in adults. And this is especially true of younger children, who haven’t yet been included in completed trials.

“Children’s immune systems sometimes act slightly differently than adults’ when they’re given the same vaccine,” says James Campbell, a pediatric infectious disease specialist at the University of Maryland School of Medicine who also runs clinical trials at the school’s Center for Vaccine Development and Global Health. This is because kids’ immune systems are busy maturing from before birth through mid-childhood.

And although most vaccines work equally well in adults and children, some, such as the pneumococcal vaccine, aren’t effective in children under age 2. (That vaccine, however, is of a different type than the ones authorized for Covid-19.) Others need to be given in different amounts or spaced differently when given to younger kids versus adults.

Most experts do expect younger children will respond well to Covid-19 vaccines. But even then, they’ll still want to find the optimal doses and dose spacing for these immunizations at each age group. This might be different for, say, a 6-month-old than for a 16-year-old.

How scientists are testing Covid-19 vaccines in children

To learn how vaccines work best in kids, scientists usually study them in different age groups. For Covid-19, researchers are working backward down the age ladder.

Starting trials in teenagers makes sense for a number of reasons. First, “adolescents are more likely to experience a similar safety profile and immune response as adults than very young children,” Moffitt explained.

Second, this age group is more likely than younger children (except for infants) to become severely ill and die of the disease.

And, third, data so far suggests that this age group has been more responsible for spreading the virus than younger children, Moffitt explained.

So after studies have gathered enough data from adolescents, researchers can be more confident testing the vaccine in younger age groups. “A vaccine that was safe in 12-year-olds is more likely to be safe in 6- to 11-year-olds than one that has only been tested in adults,” Moffitt said. Likewise, “a vaccine that’s safe in school-aged children is more likely to be safe in toddlers.”

For the youngest children, figuring out not only the best dosing but also when to administer the test vaccines could be tricky.

“Infants and toddlers have a very busy vaccine schedule,” says Campbell, who also helped develop the National Institutes of Health’s pediatric vaccine trial protocols. So researchers need to figure out if they are going to lump the trial Covid-19 vaccine doses in with regular vaccine visits (which can generate their own passing side effects) or administer them between other vaccines (which sometimes fall just a month apart for newborns).

One bit of luck is that children’s vaccine trials can be much smaller than the adult trials. In addition to seeing who among participants naturally got sick with Covid-19, adult vaccine trials have been measuring immune response to the vaccines (by looking for antibodies in the blood).

This immune response data provides a reliable shortcut for trials in kids, showing researchers what a successful immune response to the vaccine looks like. So pediatric studies are looking for similar responses in children to assess whether it is effective in preventing Covid-19, rather than having to wait for dozens of them to come down with the disease.

So whereas each phase 3 adult trial had to enroll tens of thousands of people to find enough naturally occurring infections in a few short months, “as we are only measuring immune response in adolescents, we can get those answers with many less participants,” Robert Frenck, director of vaccine research at Cincinnati Children’s Hospital, wrote to Vox in an email. As such, the companies can do studies at less than a tenth of the scale.

The new Pfizer/BioNTech trial tested the vaccine against a placebo in 2,260 adolescents. In those who received the shot, the companies say a robust antibody response was seen, equating, they say, with 100 percent efficacy — an even better result than in those ages 16 to 25, the company reported in a press release. The company said no safety concerns emerged and side effects were similar to those seen in young adults.

In addition to apparently universal antibody coverage, the Pfizer vaccine’s efficacy also seemed to play out in the real world. Eighteen of the adolescents in the placebo group ended up getting Covid-19, but none in the vaccinated group.

And the FDA has cleared vaccine makers to rapidly expand testing in younger ages. Pfizer and Moderna both have early-stage studies underway in participants as young as 6 months. Pfizer is structuring research based on age group cohorts: 5 to 11 years, 2 to 5 years, and 6 months to 2 years, testing different doses in each.

The first experimental shots were given to kids in the 5- to 11-year-old age group last week, and they plan to give the first ones in the 2- to 5-year group next week, the company reported.

Moderna announced earlier this month that it has also started administering the vaccine to its pediatric trial participants younger than 12. Although early data is expected by this summer, it plans to also follow kids for a year after their shots to track longer-term efficacy and safety.

Will kids get the Covid-19 vaccine before the next school year?

Even if a Covid-19 vaccine hasn’t been authorized or distributed for most children by the end of the summer, it might still be possible to safely send students back to school. “If you are in a situation where you have drastically reduced mortality, you have covered the most vulnerable people, you have vaccinated the teachers, and have scaled up targeted testing for schoolchildren, you have a viable way of opening schools,” says Saad Omer, an infectious disease specialist at the Yale School of Medicine.

And getting kids safely back to in-person learning will be incredibly important to prevent further disparities from emerging and get education back on track. For younger children especially, they “have a shorter window for development, where if they miss it, there are long-term consequences,” says Omer, who was on the National Academy of Medicine committee that recommended children for phase 3 vaccine priority.

But the ultimate goal will be to have children vaccinated against the virus, and as soon as safely possible. So the leading vaccine companies are working hard to get the necessary approvals. Pfizer says it hopes it will be possible “to vaccinate this age group before the start of the next school year,” CEO Albert Bourla said in a press statement.

And the CDC is paying attention. Its Advisory Committee on Immunization Practices “is closely monitoring clinical trials in children and adolescents,” according to a December paper.

Many experts are optimistic that vaccines will be authorized for children as solid data comes in. “I think a good antibody response — with a good safety profile — in kids will be sufficient to have a vaccine candidate licensed,” said Frenck, who has worked on the Pfizer vaccine trials of 12- to 15-year-olds.

Omer agrees. “You don’t have to complete the trial. Even initial preliminary data may suffice.”

But it is still unclear if most children under the age of 16 will be able to be vaccinated before the start of the next school year. And the order in which children will be eligible for an approved vaccine will likely follow the sequence of trials, with adolescents coming first. “If we can at least get down to the older kids, it would be great,” Campbell says.

One big question still hangs in the balance about the utility of vaccinating all children, however. A lot of the impetus to vaccinate children has been not just to reduce incidence of the disease in that group but also to reduce kids’ role in spreading the disease. However, we still don’t have thorough information on how well the vaccines do this.

Early data suggests the vaccines might reduce the rate at which people carry the virus without getting sick. But we are still waiting for more details from the adult studies. “The most likely scenario is that you’re going to get the best protection against the most severe disease, 95 percent protection against all disease, and slightly lower protection against all infection,” Campbell says. (This thinking also helped inform the CDC’s March guidelines for fully vaccinated people.)

Even this level of protection, however, could go a long way in improving children’s lives — and those of their parents. It could allow them to much more safely play with friends and participate in more normal activities.

What should we do before a Covid-19 vaccine is available for kids?

Covid-19 continues to spread, with new worrying upticks in cases, hospitalizations, and deaths in several regions across the country. And kids remain vulnerable to getting the illness and to spreading it to others of any age.

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So instead of having chickenpox-style Covid-19 exposure parties for kids, which can be dangerous, public health experts advocate continued vigilance against the virus. The CDC recommends children follow similar guidelines to unvaccinated adults. They should wash their hands frequently, avoid or limit contact with unvaccinated people outside their household, avoid those at high risk for the illness, wear a mask in public starting at age 2, have high-touch surfaces and toys disinfected frequently, and avoid unnecessary travel.

But with the early encouraging news from the first Covid-19 vaccine kids trial, we have more reason to expect shots for kids will be coming.

In the meantime, there’s no time to waste in helping prepare pediatricians and families for the vaccines’ arrival for kids, Campbell says. A January survey by the National Parents Union found that only about 35 percent of parents would immediately immunize their children against the disease, and almost a quarter would not get the shots for them at all. If a vast number of kids aren’t vaccinated, they could become a reservoir for the virus, spurring future outbreaks.

But Campbell is hopeful that time and experience will help resolve some of this reluctance. By the time these shots are available for kids, in addition to strong results from pediatric studies, he hopes many of the current questions and wariness around the new vaccines will also be soothed by the months of success in adults.

Katherine Harmon Courage is a freelance science journalist and author of Cultured and Octopus! Find her on Twitter at @KHCourage.