UPDATE 1-EU drugs regulator says data supports vaccine boosters after three months

* Data shows bringing forward third vaccine shot is effective

* Vaccine makers required to submit Omicron lab tests

* EMA sees no safety concern from inoculation of U.S. children (Adds details on Omicron tests, more Cavaleri quotes)

By Ludwig Burger and Pushkala Aripaka

FRANKFURT, Dec 9 (Reuters) - The European Union's drugs regulator said it could make sense to administer COVID-19 vaccine boosters as early as three months after the initial two-shot regimen amid "extremely worrying" infection numbers in the region.

"While the current recommendation is to administer boosters preferably after six months, the data currently available support safe and effective administration of a booster as early as three months from completion," the European Medicines Agency's (EMA) Head of Vaccines Strategy, Marco Cavaleri, told a media briefing.

Preparations were in full swing for the review of any redesigned vaccines that target the new Omicron variant, should it be needed, but the spread of the dominant Delta variant should for now be front and centre of the fight against the current wave, he said.

"The immunological situation remains extremely worrying in Europe," said Cavaleri. "(Delta) will remain the main focus of public health actions to cope with the pandemic and its consequences." he added.

The EMA executive said vaccine makers were required to submit results of laboratory tests to determine the level of neutralising antibodies generated by their shots against Omicron, part of the fact-finding to determine the need for vaccine upgrades.

Partners BioNTech and Pfizer on Wednesday became the first vaccine developers to publish such data, saying a three-shot course of their vaccine was able to neutralise Omicron.

Cavaleri also said that so far no safety concerns have emerged from the vaccination campaign among five to-11 year-old children in the United States, where more than 5 million in that age group have received at least one shot.

The World Health Organization, meanwhile, said on Thursday that vaccines provided a robust level of protection against severe disease for at least six months for most people.

It said administering primary doses to people in poorer countries should be the priority, and so for the time being was only recommending third doses for people with underlying health issues or who had received an inactivated vaccine.

(Reporting by Ludwig Burger and Pushkala Aripaka; Editing by Kirsten Donovan and Alex Richardson)