The only sure way for kids to safely leave masks at home is to get them vaccinated. Pfizer hopes to have its vaccine for kids as young as 2 approved in September. Meanwhile, Cambridge-based Moderna has been conducting vaccine trials on children between the ages of 6 and 11 and is expanding testing to include younger kids.

UMass Medical School in Worcester is one of the locations where the Moderna COVID-19 vaccine trials with children are underway. They’re now recruiting families with children between the ages of 2 and 6, and will soon progress to babies as young as 6 months.

GBH News spoke to Dr. Katherine Luzuriaga, a pediatric infectious disease specialist who is running those trials.

#1 Is the vaccine safe?

Yes, says Dr. Luzuriaga. Studies on adults and teens show the vaccine is safe for children in trials. “Data from the adult and teen studies have been used to design the pediatric trials, including choice of vaccine doses to be studied and the conduct of safety evaluations,” said Luzuriaga.

“We try to safeguard not only the child’s physical health, but also their mental well-being,” said Luzuriaga. For example, researchers try to minimize the number of blood draws.

In addition to looking for any of the adverse reactions that had been reported in adults and teens, the study’s team keeps close contact with the children and families, even if it means a call in the middle of the night. And, Luzuriaga said, follow-up with the children continues after regulatory approvals.

Luzuriaga also said mRNA vaccines such as Moderna's are unlikely to be "associated with long-term safety issues” because they don’t integrate into the vaccine recipient’s DNA.

#2 How do you determine the vaccine dose to give children?

Researchers use what’s commonly called a "Goldilocks" approach to get to the right dose: not too big, and not too small.

“We start with smaller numbers of older kids — 6 to 11 years — at the lower doses. And if they tolerate that, we go to the next higher dose. And if the safety profile is acceptable after that first dose, then we can begin that dose in a certain number of kids,” said Luzuriaga.

That same stepping up and down approach would then be used in the 2- to 6-year-old group, and later in 6 month to 2-year-olds.

#3 Which young children are best suited to test COVID-19 vaccines?

Children taking any medication that could raise safety issues or would interfere with the ability to generate an immune response — such as high dose steroids — are ineligible. Behavior is also considered.

“We ask parents about their children and how they handle new situations, exposure to new folks,” said Luzuriaga. “If a child is extremely shy or hesitant, [or] doesn't really deal with strangers very well, that child might not be the best child to enroll in the trial.”

#4 What side effects could children experience?

Researchers are hoping the vaccine will raise similar immune responses to those seen in adults and teens. They're also looking for reactions and side effects similar to those seen in older groups — including pain or swelling at the injection site, fever, fatigue and body aches. Those side effects mean the vaccine's likely working, though not experiencing side effects doesn't mean the vaccine isn't working.

“Sometimes in young children, that's a little more difficult to discern. A 2-year-old might not necessarily say, ‘I have a headache or my joints are aching,’ but there are age-specific things that we look for — like a certain amount of irritability,” said Luzuriaga.

#5 Do we really need to vaccinate young kids?

Kids may not show symptoms or get as severely ill as adults with COVID-19 do, but they can become infected and some kids get very sick.

“We've seen them in the hospital, and we’ve seen some with serious conditions like multi-symptom inflammatory syndrome,” said Luzuriaga. “And if we want to do our best to limit community spread in schools, in families — we need to immunize children.”

#6 Do kids need masks at school and camp until there’s a vaccine for them?

Students in Massachusetts will return to in-person learning in the fall. While high school and middle school students won’t need to be masked, a decision about whether or not to require masks for younger children will be made by officials over the summer. But until vaccines become available for younger children, keeping them masked in school is a good idea, said Luzuriaga.

“What we know is that if kids are masked, and social distancing and hygiene recommendations are followed, that there is very little spread in school,” said Luzuriaga. “We’re highly encouraging teachers and other adults who are eligible for vaccination, for anybody working with the kids, to be vaccinated.”

Luzuriaga recognized that masking, social distancing and hygiene can be hard for kids, but it’s worth the effort for the time being.

“We realize it is tough to do,” Luzuriaga said. “But again, hopefully it won't be for too long before we are able to vaccinate the kids.”