As the first vaccines against COVID-19 are being distributed, there’s been a lot of conversation about who will be at the front of the line for the shot. But there is one group that’s not eligible: Kids.

Here’s a look at why this is, when it will change and what the implications are for reopening.

The first COVID vaccine has been approved. Can kids get it?

Right now, the Pfizer and BioNTech vaccine has only been approved for individuals 16 years and older.

Last month, the American Academy of Pediatrics put out a call for vaccine trials to start including kids. Now, those trials are getting started, but only for older children, ages 12 and above.

“We know children aren't little adults, and so we need to know how they're going to respond and react to this vaccine,” said Sally Goza, president of the American Academy of Pediatrics.

She wants a vaccine for kids to be available by next school year and, she said, that means trials would need to start soon.

More than 1 million kids have already been infected with the virus. “And we also know that children suffer in other ways from this virus, from the social isolation, from not being able to go to school, food insecurity, housing insecurity, all of those things are affecting our children,” Goza said.

Despite calls to move quickly to begin testing the vaccine on children, it’s standard practice that when a new vaccine is ready for testing in humans it is first tried in healthy young adults. If something goes wrong, their bodies are the best equipped to respond.

After the COVID vaccine was proven to be safe and effective in healthy young adults, the elderly were next in line.

“Because of the urgency of the pandemic, we immediately went to the highest risk population, which is, of course, the older adult,” said Rick Malley, a professor of pediatrics at Harvard Medical School and a doctor in the Division of Infectious Diseases at Boston Children’s Hospital.

After the highest-risk populations are addressed, “gradually the vaccines are studied in lower and lower and lower age groups,” he said.

Why are vaccines tested separately in kids and adults?

“The reality is that the immune system is not a static system. It is evolving as the individual ages,” said Malley. “It's very different when you are a newborn compared to a young infant, compared to a toddler and so on and so forth.”

He says studying each age group is key to learning about different side effects and the correct dosage. Plus you really need to make sure the vaccine is not going to cause more problems than the virus causes, and that varies by age.

“Because children are at such lower risk of severe complications from COVID-19, the bar of acceptability of serious adverse events from the vaccine has also got to be higher,” Malley said.

When will a COVID vaccine for kids be available?

Nobody knows exactly.

Malley expects vaccine trials in kids to be rolled out over the next year, sequentially getting to younger and younger age groups.

Lloyd Fisher, head of the Massachusetts Chapter of the American Academy of Pediatrics and a local pediatrician, said once the shot is approved, he is not too worried about vaccine distribution.

“The great thing about Massachusetts is we have a very strong immunization program. Our state already supplies all of the vaccinations for everyone under 19 years,” Fisher said. “We have a very good distribution network of vaccines coming from the State Department of Public Health to our pediatric and family medicine practices where children receive care.”

By that time, he added, we should have worked out a good system for keeping the vaccines cold.

What are the implications for reopening schools?

Experts are hopeful that not having a COVID vaccine approved for kids will not significantly delay getting kids back into classrooms.

“In general, we believe that schools have not represented a major source of super-spreading events or onward transmission,” said Malley.

Plus, he said, as more and more adults get vaccinated the amount of the virus in a community will hopefully get to a very low level.

Combine those two facts and, he said, there hopefully won’t be much concern about kids going to school even if they are unvaccinated.

When kids do get the vaccine, can they go back to playing like they did before the pandemic?

No, not yet.

Once children start getting the vaccine, we know it will make that individual kid a lot less likely to get sick, but we still won’t know how long that protection will last or whether the vaccinated kid will be able to transmit the virus to someone else, even if they don’t get sick from it.

So, kids — like adults — will still need to keep wearing masks, social distancing and avoiding crowded spaces. A vaccine for kids will make things a whole lot better, but it doesn’t mean things will return to pre-pandemic normal, at least not yet.