An expert panel will weigh authorization of Pfizer Inc PFE.N and BioNTech's COVID-19 vaccine for U.S. children aged 5 to 11 on Tuesday as it prepares to vote on a recommendation for the federal Food and Drug Administration.

An authorization is an important regulatory step toward reaching about 28 million children of these ages, most of them back in school for in-person learning.

The FDA need not follow the advice of its outside experts, but usually does.

While children rarely become seriously ill or die from COVID-19, some develop complications, and COVID-19 cases in unvaccinated children have risen due to the contagious Delta variant.

The age group is "far from being spared from the harm of COVID-19," with the virus now one of the top 10 causes of deaths in American children, FDA official Peter Marks told the panel. He said there had been close to 100 deaths in that age group so far, and 1.9 million infections.

"In addition, infections have caused many school closures and disrupted the education and socialization of children," he said.

FDA staff, in documents posted before the meeting, said the likely vaccine benefits in that age group clearly outweigh the potential harms, including the rare risk of heart inflammation.

Only a few other countries, including China, Cuba and the United Arab Emirates, have cleared COVID-19 vaccines for children in this age group and younger.

Since May, the World Health Organization has been urging rich countries to reconsider plans to vaccinate children and instead donate COVID-19 shots to the COVAX scheme for poorer countries.

The advisers are expected to pay close attention to the rate of the rare cases of heart inflammation called myocarditis that have been linked to both the Pfizer/BioNTech and Moderna MRNA.O vaccine, particularly in young men.

Pfizer and BioNTech are seeking clearance for a lower, 10-microgram dose version of the vaccine in children, versus 30 micrograms for everyone over the age of 12. The shot has been authorized for ages 12-15 since May and cleared for everyone over 16 since December.

The companies have said their vaccine showed 90.7% efficacy against the coronavirus in a clinical trial of children aged 5 to 11. 

After the FDA, a panel to the U.S. Centers for Disease Control and Prevention will make a recommendation on the administration of the vaccine. The director of the agency will make the final call.

Top U.S. infectious disease expert Anthony Fauci said on Sunday that it was likely the vaccine will be available to children in the first week or two of November. 

If the number of myocarditis cases in the younger age group turns out to be similar to that in 12- to 15-year-olds, the hospitalizations prevented for COVID-19 would outnumber those prevented for myocarditis in most scenarios analyzed, FDA staff reviewers said.

"No matter what size of the safety database, there will always be uncertainties regarding benefits and risks, including for example, the risk of vaccine-associated myocarditis," said Doran Fink, the FDA's deputy director for vaccine development.

These uncertainties have to be addressed in surveillance data and studies following authorization, Fink told the panel.

Pediatric vaccinations are an important public health tool to prevent infectious diseases, even ones that do not cause high rates of mortality or hospitalization for children.

(Reporting by Manas Mishra in Bengaluru and Michael Erman in New Jersey; Editing by Caroline Humer, Richard Chang and Jonathan Oatis) ((Manas.Mishra@thomsonreuters.com; www.twitter.com/Manasmishra24))