CNN  — 

Americans 12 and older can get a Covid-19 vaccine, but younger children are still waiting.

With many schools across the United States now just weeks from reopening for the fall semester, pharmaceutical companies Pfizer and Moderna are still doing clinical trials to see how coronavirus vaccines work in children under 12 – if they’re safe and what the right dose should be.

Meanwhile, all but four states are seeing an increasing trend in cases, with doctors describing patients who are younger and sicker than what they saw in the winter.

The surge in cases has many parents of children under 12 asking when their little and not-so-little ones can get the vaccine. The answer is that it’s going to be months, if not longer. It’s not as simple as administering available adult doses to younger people.

“I understand parents’ concern in wanting their children to get vaccinated, but we have to make sure we’re doing the best and safest thing for children,” Dr. Chip Walter, a pediatrician at Duke University and an investigator for the Pfizer trials, said.

When we might be able to vaccinate children under 12

Pfizer’s vaccine study is enrolling more than 4,600 children in three age groups: 5-to-11-year-olds; 2-to-5-year-olds; and babies 6 months up to age 2.

Data for children 5 to 11 could come sometime in September and depending on the findings, the company told CNN it could ask the US Food and Drug Administration to authorize emergency use of the vaccine that same month.

Data for 2-to-5-year-olds could arrive soon after. For the youngest children, Pfizer said it could potentially get data in October or November, and shortly thereafter ask the FDA to authorize emergency use.