But even when those vaccines hit the market, they will not be available to children. That’s because very few children have been part of the clinical trials to date. Pfizer only recently began enrolling children as young as 12…

“Children are not just small adults,” said Dr. Sallie Permar, a professor of pediatrics, microbiology and immunology at the Duke University School of Medicine, in an interview with NPR’s All Things Considered.

A child’s immune system is different from an adult’s, Permar said. “There are certain vaccines that work better in children than adults. And there are certain vaccines that work less well in children compared to adults,” she said. “So they do have to be specifically studied in the pediatric population.”