Japan has agreed with Pfizer Inc. to purchase an additional 10 million COVID-19 vaccine doses by March, the health ministry said Monday, as the county trails other developed economies in its rollout of booster shots.

The additional shots will add to the 120 million doses Japan already agreed to procure from the U.S. pharmaceutical giant for this year.

"The government will continue to negotiate with vaccine makers to ensure steady progress on speeding up administering booster shots," Shigeyuki Goto, minister of health, labor and welfare, told reporters.

The deal came as Prime Minister Fumio Kishida has pledged to administer a million booster shots per day to mitigate the delay in the rollout.

The government has opened mass vaccination centers in Tokyo and Osaka, operated by the Self-Defense Forces, to speed up its efforts.

The percentage of people in Japan who have had their third jab stood at 7.9 percent as of Thursday, according to government data, far behind Britain, France, and Germany, where over 50 percent of the population has had a booster shot.

Besides Pfizer's vaccine, Japan has agreed to buy 93 million shots and 150 million shots this year from U.S.-based drug companies Moderna Inc. and Novavax Inc., respectively.