Two 13-year-old brothers are participating in Moderna's vaccine trial for kids. They're 'pretty chill' about it.

• Emmett and Gavin Preston, 13-year-old brothers, are participants in Moderna's vaccine trial.
• Moderna is studying the effects of its coronavirus shot among 3,000 kids from 12 to 17.
• The brothers said they didn't want to spread the virus to their mom, who has an autoimmune condition.

At 13 years old, Emmett and Gavin Preston aren't yet eligible to receive a coronavirus vaccine. The Food and Drug Administration hasn't approved the shots for kids under 16 due to a lack of data.

But the Preston brothers are participants in Moderna's clinical trial: The company is currently studying the effects of the shot among 3,000 kids ages 12 to 17. A separate trial is testing it in 6,750 children under 12, including babies as young as six months.

Emmett and Gavin, both adopted, received their first shots on February 12 at their local doctor's office in Charleston, South Carolina, then their second shots one month later. The brothers said they were a bit nervous about the needle but haven't felt many side effects.

"When they showed me the shot, I was like, 'What?' And then when I took it, I was like, 'Oh, that's not that bad,'" Emmett told Insider.

For a week after each dose, they logged their symptoms into an app so researchers could track their side effects.

"I just felt like my normal self," Emmett said. By the second time he got vaccinated, he added, he was "pretty chill" about it.

Kids may respond differently to the vaccine than adults

Moderna's trials are randomized, double-blind studies, meaning half of the participants get the vaccine while the other half get a placebo, and nobody knows which they've gotten.

For some adult participants, side effects were sometimes a clue that they'd gotten more than a saline solution - some felt headache, fever, or chills (indicators that their bodies were reacting and building antibodies). But scientists aren't sure whether kids will feel side effects to the same degree.

"Children generally respond well to vaccines," Donna Farber, a Columbia University immunologist, previously told Insider. "They should respond well or comparably to a young adult - and maybe even better."

Emmett said he had a sore shoulder and "felt a bit run down" after the first shot. Gavin said he had some minor fatigue two days after the second one.

"It went perfectly after all that," Gavin said. "Nothing has really happened."

In general, kids aren't very susceptible to severe illness due to COVID-19. Children represent around 13% of confirmed coronavirus infections in the US, but less than 0.2% of the nation's coronavirus deaths. Some researchers suspect that's because kids' immune systems fight off the virus before it has a chance to replicate widely.

The Preston brothers were on board with the trial right away

Children can be difficult to include in trials, since ethical questions arise if they don't fully understand what they're signing up for, and scientists are cautious of any research that could stunt a child's development. Many parents are not comfortable signing their kids up to participate for the same reasons.

But the Preston brothers are no strangers to clinical trials. For the past few years, they've participated in the Adolescent Brain Cognitive Development Study, the largest long-term study of brain development and child health in the US. The study recruits healthy children ages 9 to 10 and observes their brain growth through early adulthood.

So when the Preston boys' mother, Katie, approached them about getting the Moderna vaccine, they didn't think twice about it, they said.

"My mom brought it up and I was like, 'Ooh, that sounds interesting,'" Emmett said.

Katie said she learned of the trial through a friend who posted about it on Facebook. She emailed her doctor's office in Charleston to express interest, then heard back a few weeks later.

"We had to go through a little screening process and they said the boys were good, so we went for it," Katie said.

Emmett and Gavin are less stressed about in-person school now

The Preston brothers were motivated to get vaccinated as soon as possible because Katie has an autoimmune condition and both boys have returned to school in-person. They didn't want bring the virus home.

Coronavirus transmission tends to be low in schools, as long as masks and social distancing are mandatory, but kids can still spread the virus, even if they have no symptoms.

"Just being able to protect myself and my family from coronavirus really makes me feel positive inside," Gavin said.

He added that he was eager to assist with scientific research, since science is one of his favorite subjects.

When he grows up, he said, "I want to research dementia, Alzheimer's, anything memory loss related, to try and help those people."

Knowing that there's a 50-50 chance they're vaccinated, both brothers said, has made them less stressed about getting sick at school. Neither wants to return to virtual learning.

"It was really hard to learn online," Gavin said. "Then when I got in school, my grades started to go up."