Pfizer Inc. said Monday its COVID-19 vaccine was safe and effective for children aged between 5 and 11 following clinical trials that showed participants had a strong immune response against the virus.

The U.S. pharmaceutical firm and its German vaccine development partner BioNTech SE will submit the data to U.S. and other regulatory authorities in the near future to seek approval for use. The vaccine is currently administered to people aged 12 and older in Japan and overseas.

Supplied photo shows a tray of Pfizer Inc.'s COVID-19 vaccines. (Photo courtesy of Pfizer Inc.)(Kyodo)

In the clinical trials, a two-dose regimen of 10 micrograms, one-third of the amount used by older people, was administered 21 days apart to 2,268 children aged 5 to 11.

The results showed the antibody responses in the participants were similar to those found in people aged 16 to 25 in a previous study, with the side effects generally comparable to those observed in the participants in the older age group, the companies said.

"We are eager to extend the protection afforded by the vaccine to this younger population, subject to regulatory authorization, especially as we track the spread of the Delta variant and the substantial threat it poses to children," Pfizer Chairman and Chief Executive Officer Albert Bourla said in a statement.

In Japan, Chief Cabinet Secretary Katsunobu Kato said a health ministry panel will study whether to lower the age limit to include those under 12 after the safety and effectiveness is confirmed by the Pharmaceuticals and Medical Devices Agency, the Japanese vaccine screening body.

"While infections of children draw strong interest as schools restart, we need to confirm the safety and effectiveness of the vaccine," Kato told a press conference. "We will respond appropriately as the Health, Labor and Welfare Ministry continues to gather information."

Pfizer and BioNTech are also conducting clinical trials for children under 5 years old and they are expected to announce the results later this year, they said.