Pfizer says three small doses of its COVID-19 vaccine protect children under the age of 5 and that it plans to give the data to U.S. regulators later this week.

It's the latest step toward letting the littlest kids get the shots.

Data from Pfizer showed that the three-dose vaccine was 80% effective against omicron infection among children between 6 months and 5 years of age.

However, researchers at the company said the data was preliminary and a larger trial is needed to see how the three-dose vaccine fares against severe disease.

The 18 million tots under 5 are the only group in the U.S. not yet eligible for COVID-19 vaccination.

The Food and Drug Administration has begun evaluating data from rival Moderna.

That company hopes to offer two kid-sized shots by summer.

The FDA has set tentative dates next month for its scientific advisers to publicly debate data from Pfizer and Moderna.