Japan has been in talks with U.S. pharmaceutical giant Pfizer Inc. about the possibility of moving up the schedule to receive its COVID-19 vaccine doses as the nation steps up its booster shot drive, Prime Minister Fumio Kishida said Thursday.

Japan is due to receive 120 million doses for 2022 from Pfizer, which said Wednesday a third shot of its coronavirus vaccine could offer sufficient protection against the new Omicron variant of the virus.

"Currently, we are negotiating (with Pfizer) whether the supply schedule can be brought forward," Kishida told a parliamentary session, responding to a question from an opposition lawmaker.

A senior citizen receives the Pfizer coronavirus vaccine at a vaccination center in Kobe, western Japan, on May 25, 2021. (Kyodo) ==Kyodo

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Pfizer's COVID-19 vaccine has been approved in Japan for use as a booster, with another U.S. drugmaker Moderna Inc.'s vaccine also expected to get the green light.

Japan has set an eight-month interval "in principle" between second vaccination shots and a booster, with third doses being administered to health care workers from earlier this month and those for the elderly starting in January. But Kishida has said the government plans to shorten the interval.

The number of new coronavirus cases has fallen sharply in Japan with four cases of infection by the Omicron variant confirmed so far. After lagging behind the United States and some European nations, Japan accelerated its inoculation drive with over 77 percent of its population vaccinated twice.