When will kids get the Covid vaccines? Scientists still need to make sure they’re safe.

With the US Covid-19 vaccine supply still limited, and the rollout still slow, immunizing the country’s tens of millions of children under the age of 16 may seem very far off. Many have been left wondering if there is any chance kids will be able to get the shot before the next school year.

The finite vaccine doses — authorized by the Food and Drug Administration for people 16 and older for Pfizer/BioNTech, and 18 and older for Moderna — are currently going to the highest-priority groups to most rapidly reduce deaths. And children have been the age group least likely to die from Covid-19: The disease has killed about 190 children in the US, compared with more than 281,000 people age 65 and older.

But many kids have caught the virus, with about 2.5 million pediatric Covid-19 cases reported as of January 14 — likely a substantial undercount because these cases are often mild or asymptomatic. More than 10,000 kids have been hospitalized for the illness as well. There have also been more than 1,600 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 falls before the general adult population and in the same group as many essential workers. The Centers for Disease Control and Prevention has not yet decided what group it will put children in.

But even as we weigh how to prioritize them, we also have yet to ensure the vaccines are effective and safe in children, whose immune systems can work slightly differently than adults’.

Vaccine companies are racing to gather vaccine data in kids. Pfizer/BioNTech, in their phase 3 trial, gave their vaccine to children ages 12 to 17, and data from this age group will continue to be gathered and analyzed. Moderna is enrolling youth in this same age group for a study.

While companies and regulators are working to have pediatric-approved vaccines ready before the next school year, it’s also crucial that the research in kids proceed carefully.

Here’s where we are in learning about the Covid-19 vaccines in children — 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

Fortunately, we now have a 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 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.

“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 pneumococcus vaccine, aren’t effective in children under age 2. (That vaccine, however, is of a different type than the ones approved for Covid-19.) Others need to be given in different amounts or spaced differently when given to kids versus adults.

Most experts do expect 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 newborn than for a 16-year-old.

How scientists will test 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 from 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, “trials will likely progress to younger and younger age groups,” Moffitt said. “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,” she 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 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 — and hopefully faster — than the adult trials. That’s because, 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 future trials, showing researchers what a successful immune response to the vaccine looks like. So pediatric studies will look 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 goal is to enroll about 2,000 teenagers, he says.

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 has been testing the shots in children 12 and up for months, and has now gathered a decent amount of data. Campbell expects the company to include ages 12 and up in its application to get the vaccine licensed. And younger age groups should follow. “Moderna is close behind, and they have a similar approach,” he says. AstraZeneca has plans to include children in trials as well.

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 approved 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 — or any — children will be able to be vaccinated before the start of the next school year. Even if kids get approval, they may have to wait in line behind other priority groups, and limited supplies could make rapid, mass vaccination of children challenging.

The order in which most 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. Getting the vaccine to children with underlying health conditions will also likely be a high priority.

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.

Even this level of protection, however, could go a long way in improving children’s lives — and those of their parents. “Vaccinating children can help them go back to school, see their grandparents, play with friends,” he says.

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

Covid-19 continues to spread at a deadly pace, especially with seemingly more contagious variants taking off across the country. And kids remain vulnerable to getting the illness and to spreading it to others of any age.

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 adults. They should wash their hands frequently, avoid or limit contact with 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.

And because we don’t yet have solid information on how well the vaccines prevent virus transmission, people who have already gotten their two vaccine doses should still take precautions — like mask-wearing and distancing — around those who are unvaccinated. This includes grandparents who have gotten their shots and are considering spending time with children and grandchildren they haven’t been in social bubbles with. Although vaccinated older folks are at reduced risk of severe illness themselves, they might still be able to pass the virus to children or others in the household.

“It’s important vaccinated individuals remain vigilant about preventing transmission,” Moffitt said. Once most people are vaccinated — kids included — we should be able to get back to more normal social interactions.

So there’s no time to waste in helping prepare pediatricians and families for the vaccines’ arrival for kids, Campbell says. A December survey by the National Parents Union found that only about 30 percent of parents would immediately immunize their children against the disease, and about a quarter would not get the shots for them at all. If a vast majority 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 months of success in adults.