Coronavirus vaccines may be available in the fall for U.S. children as young as 6 months, drugmakers say. Pfizer and Moderna are testing their vaccines in children younger than 12 years old, and are expected to have results in hand for children ages 5-11 by September.

Compared with adults, children are much less likely to develop severe illness following infection with the coronavirus. But nearly 4 million children in the United States have tested positive for the virus since the start of the pandemic, according to the American Academy of Pediatrics.

Doctors continue to see rare cases of multisystem inflammatory syndrome in children, a condition linked to COVID-19 that can affect multiple organs, including the heart. Vaccinating children should further contribute to containment of the virus by decreasing its spread in communities.

Pfizer announced Tuesday that it was moving to test its vaccine in children ages 5-12 years. It will begin testing the vaccine in infants as young as 6 months in the next few weeks.

The company hopes to apply to the Food and Drug Administration in September for emergency authorization of the vaccine for children ages 5-11. Results for children ages 2-5 could be available soon after that, according to Kit Longley, a spokesperson for Pfizer.

Data from the trial for children between 6 months and 2 years old could arrive in October or November, followed by a potential submission to the FDA shortly thereafter, Longley added.

The Pfizer-BioNTech vaccine was authorized last month for use in children ages 12-15.

Based on data from an earlier study that assessed safety, Pfizer will give two doses of 10 micrograms each — a third of the dose given to adolescents and adults — to children ages 5-11, and two doses of three micrograms each to children 6 months-5 years.

The study will enroll up to 4,500 children at more than 90 clinical sites in the United States, Finland, Poland and Spain. Pfizer's researchers plan to submit the full data from the trials this summer for publication in a peer-reviewed journal.

As vaccine eligibility widens, the White House has launched a monthlong blitz to combat vaccine hesitancy and a lack of urgency to get shots, particularly in the South and Midwest.

But the U.S. is unlikely to meet President Joe Biden's target to have 70% of Americans at least partly vaccinated by July 4.