The US Medicines Agency (FDA) has authorized the booster dose for this age group "to provide continued protection against Covid-19", she explained in a press release.
A committee of experts from the Centers for Disease Control and Prevention (CDC) is due to meet Thursday to consider the issue in turn, and recommend this booster dose.
It must be injected at least 5 months after the first series of two injections.
The dosage used is 10 micrograms, both for the initial injections and for the booster dose (compared to 30 micrograms for ages 12 and older).
This authorization comes at a time when the United States is recording an increase in the number of cases of Covid-19, with around 90,000 us cases declared per day.
Hospitalizations are also on the rise.
Covid-19 "tends to be less severe in children than adults," FDA chief Robert Califf said in the statement.
But "the wave linked to the Omicron variant has made more children sick and led to more hospitalizations and children suffering long-term effects", he underlined.
The United States has 28 million children between the ages of 5 and 11.
Among them, more than 4.8 million cases have been counted, and some 360 deaths, according to CDC figures.
This age group has been eligible for vaccination with Pfizer since November 2021, but less than 30% of them are fully vaccinated.
The FDA again on Tuesday stressed the importance of vaccination to prevent serious cases of the disease.
Americans over 50 are already eligible for a second booster dose (fourth dose in all).
Children under 5 are not yet eligible for vaccination, with no vaccine, but a committee of independent experts is due to meet in June to review clinical trial data from Pfizer and Moderna for a authorization for this age group.
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