COVID-19 vaccine pediatric trials are currently taking place in dozens of cities across the country. In Chicago, doctors at Lurie Children’s Hospital are studying immunization results in children aged 6 months to 5 years, the Chicago Tribune reports.

According to the American Academy of Pediatrics, over 7 million American children have been infected with COVID-19. Researchers across the country are using trials, like the one taking place at Lurie Children’s Hospital, to examine whether the vaccine is safe and effective for kids under 5.

Doctors at Lurie Children’s Hospital started running COVID-19 vaccine tests on children in February, and they are still actively recruiting new participants, Chicago Tribune reports. Close to 120 Chicago-based kids and infants are already participating in the Moderna vaccine study at the children’s hospital. Half of them are under 2 years old and the other half are between the ages of 3 and 5.

According to the outlet, each volunteer gets one shot of either a low dose of the Moderna vaccine or a placebo. Then, they return four weeks later to receive their second dose. The children and their parents don’t know whether they’ve received the vaccine or a placebo because the study is blinded. However, 75% of participants in the study at Lurie are given the Moderna vaccine.

“We are very careful about appropriate testing and appropriate follow-up,” Dr. Bill Muller, professor of pediatrics at the Feinberg School of Medicine and an infectious disease specialist at Lurie Children’s Hospital told the Chicago Tribune. “Being a part of a trial is very different from being a part of regular clinical care. In one way, it’s a little bit more experimental. In another way, we’re paying a lot more attention. So that might make people feel a little more reassured.”

Dr. Muller understands that infants and kids are “less likely to have severe disease from COVID.” But he’s also aware that more data needs to be collected on the long-term physical effects of the virus on infected children. “One day in a hospital is a pretty bad thing for a kid,” he told the Chicago Tribune. “We talk about death as being uncommon, which is fortunate. But even serious illness is a pretty significant thing for a child.”

Pfizer CEO Albert Bourla recently told NBC News that there should be enough data on the Pfizer vaccine in children under five by the end of the year. Dr. Anthony Fauci, the Director of the National Institute of Allergy and Infectious Diseases, mentioned in November that babies and toddlers aged 6 months to 5 years could be eligible to take the COVID-19 vaccine by next spring.