DURHAM, N.C. (WNCN) — Duke Health began participating in the Pfizer and BioNTech Phase 1 study — a first in the United States — in preventing COVID-19 with the vaccine among children under the age of 12.

Duke Health said Alejandra and Marisol Gerardo, twin 9-year-old girls, received their first vaccinations on Wednesday.

“The importance of safely vaccinating children against COVID-19 is twofold,” said the study’s principal investigator at Duke is Dr. Emmanuel “Chip” Walter, professor in the Department of Pediatrics and chief medical officer of the Duke Human Vaccine Institute.

“We got two small sore arms in the household right now. They both said, ‘I think that means it’s working,” their mom, Susanna Naggie said.

Naggie and the twin’s father work in healthcare and are both vaccinated. She said she had a conversation with the twins before joining the study to explain why it was important. They agreed to be part of the trials.

“They were pretty excited. They wanted to tell their friends at school. We talked to them about it requiring more testing,” Naggie said.

Little did any of them know — they’d be the very first participants in this nationwide study.

“I hope for them it will empower them to understand they were part of this and being part of scientific discovery can be a very exciting thing,” Naggie said.

Naggie says she trusts the trials are safe. She herself has participated in other clinical trials.

“We understand the importance of vaccination for us to be able to achieve the level of immunity in the community that’s needed. We identify kids as being a critical part of our community,” she said.

The first phase of the study looks at three different dosage levels, with 16 healthy children assigned to each of the three dosage levels, Duke Health said. Each child will receive two doses 21 days apart.

Alejandra and Marisol both received the lowest dose.

“Given their size and their age and they’re being the first kids at this age to receive it, there is some risk. But we honestly perceived that to be low,” Naggie said.

If the Food and Drug Administration ultimately approves a vaccine for children, Naggie knows her twins would have played a critical role.

“They’re beginning to maybe understand a little bit that what they did could really, ultimately, impact a lot of people,” Naggie said.

According to Duke Health, data on the safety and immune responses from the first 48 children will help to decide the selection of the dose level of vaccine to be used in the second study.

Duke’s participation in the study is the first phase and will enroll a total of 12 children.

“First, children can develop serious infection and the consequences of infection include death,” Walter said. “There have been more deaths in children during the past year than during a typical flu season. Second, being able to vaccinate children is an important component of developing herd immunity, or population-level protection, as children makeup a significant proportion of our population.”

Duke said they anticipate enrolling more children next week.

The FDA will likely be waiting for months for trial results for children under 16. Pfizer started enrolling children ages 13 to 16 a few months ago.

Dr. Anthony Fauci told CBS News results for children between ages 12 through 17 will likely come in the fall. Those results are not likely to coincide with the start of the school year. That timing could allow for vaccinations in high school-aged children by the end of the year.

Fauci said data on vaccines in children under 12, however, will not come until about the first quarter of 2022.

The FDA will have final discretion in whether children 16 and under are authorized for vaccinations.