Japan has been in talks with U.S. pharmaceutical giant Pfizer Inc. about the possibility of moving up deliveries for COVID-19 booster shots, Prime Minister Fumio Kishida said Thursday.

Japan is due to receive 120 million doses in 2022 from Pfizer, which said Wednesday a third shot of its coronavirus vaccine appears to 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 in response to a question from an opposition lawmaker.

Pfizer's COVID-19 vaccine has been approved in Japan for use as a booster. Moderna Inc.'s vaccine is 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 starting 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 in recent months. Four cases involving the omicron variant have been confirmed so far in passengers arriving from overseas.

After lagging behind the United States and some European nations, Japan accelerated its inoculation drive over the summer to pass most developed countries. Over 77% of the population has received two doses.