American drugmaker Moderna is asking U.S. officials to approve its COVID-19 vaccine for the nation's youngest children. Children under 5 are the only group in the United States not yet able to be vaccinated.

    Families have been waiting a long time to protect their young children, even as people are gathering in higher numbers and wearing fewer face coverings. But coronavirus variants continue to spread.

    Moderna provided its study results to the Food and Drug Administration (FDA). The drug company hopes the information proves that two low-dose shots can protect babies and young children.

    "There is an important unmet medical need here with these youngest kids," said Dr. Paul Burton. He is Moderna's chief medical officer. Two shots for children "will safely protect them. I think it is likely that over time they will need additional doses."

    Currently, Pfizer's vaccine is the only one approved for children. But that vaccine is only for children over the age of 5. That leaves 18 million young children and babies unprotected.

    Pfizer is also expected to announce whether three of its even smaller-dose shots work for very young children. The FDA said in February that the company's two doses were not strong enough.

    Some families have questioned why a shot for young children has taken so long.

    FDA vaccine chief Dr. Peter Marks told U.S. lawmakers this week that the FDA cannot evaluate a product until a producer completes its application. In a statement Thursday, the FDA said Moderna still must send some additional data to complete its request.

    "It's critically important that we have the proper evaluation so that parents will have trust in any vaccines that we authorize," Marks said.

    If the FDA approves Moderna's vaccine for young children and babies, the U.S. Centers for Disease Control and Prevention (CDC) would then have to recommend who needs it. It could either be for all young children or just those at higher risk from COVID-19.

    The FDA will face some complex questions.

    The two Moderna shots for young children are each one-fourth of the normal dose for an adult. In a study of kids ages 6 months through 5 years, data showed that the doses produced high levels of virus-fighting antibodies. It was the same amount produced in young adults, Burton said. There were no serious side effects reported, and the shots resulted in fewer high body temperatures than other usual vaccines for children.

    Moderna's vaccine proved between about 40 percent and 50 percent effective at preventing symptomatic COVID-19 during the trial. Burton said the Omicron variant's ability to partly escape vaccine immunity was a reason that effectiveness was not higher.

    Moderna's COVID vaccine so far has only been available to adults in the U.S. Other countries have already been offering the shot to children as young as 6. But months ago the FDA said it had concerns about a rare heart-related side effect in teenage boys.

    COVID-19 generally is not as dangerous for children as it is for adults. But a small number have become very sick or even died. About 475 children younger than 5 have died from COVID-19 since the pandemic's start, the CDC says. Child hospitalizations greatly increased during the spread of Omicron.

    It is not clear how many parents plan to vaccinate their young children and babies. Less than one-third of children ages 5 to 11 have had two vaccinations.

    I'm Dan Novak.