U.S. pharmaceutical giant Pfizer Inc. on Wednesday applied to Japan's health ministry for approval of its COVID-19 booster shots for children aged 5 to 11.

While third vaccine shots are widely administered to adults in Japan, children in that age group are currently only allowed to receive up to two shots.

According to Pfizer's clinical trial data released in April, its booster shots increased the amount of neutralizing antibodies, which curb virus activities, sixfold when administered to children aged 5 to 11 about six months after their second shots.

The vaccines were found to be effective for the Omicron variant of the coronavirus and no safety issues were identified, the company said.

The U.S. Food and Drug Administration authorized Pfizer's booster shots for children in the age group in May.