TOKYO: Japan began COVID-19 vaccinations for its sizable elderly population on Monday, with imported doses still in short supply and the pace unlikely to stop a fourth wave of infection.

Shots for people aged 65 and above began at some 120 sites across the country, using Pfizer Inc's vaccine made in Europe and delivered to the regions in the past week.

Just 2,810 people in Tokyo are expected to get a shot from the first batch, while most regions will receive 1,000 doses or fewer, according to a health ministry schedule. Japan has a rapidly ageing population totalling 126 million.

Chief Cabinet Secretary Katsunobu Kato reiterated on Monday the government's projection that it can secure enough vaccines for Japan's 36 million people over the age of 65 by the end of June.

"If imports from the EU go smoothly, I understand the country is expected to distribute vaccines that can be administered to all of the elderly," Kato said.

Tokyo also began on Monday a month-long period of quasi-emergency measures to blunt a fourth wave of contagion driven by virulent mutant strains and with the planned start of the Summer Olympics just over 100 days away.

Japan was among the last major economies to begin COVID-19 inoculations when it started in mid-February. Taro Kono, the minister in charge of vaccines, has defended the pace, saying local governments wanted time to prepare.

"After tomorrow, we will inform the prefectures how much we can distribute, and they will decide how much to allocate to each municipality," Kono said on national broadcaster NHK on Sunday.

Japan is dependent on Pfizer's vaccine as the only COVID-19 shot approved by domestic regulators. The pace of shots is likely to accelerate in May as a greater number of imports from the company's facilities in Europe is due to arrive.

About 1.1 million people in Japan, mostly frontline healthcare workers, have gotten at least one dose of the Pfizer vaccine's two-shot regimen so far. Prime Minister Yoshihide Suga is among some 90 bureaucrats who were vaccinated ahead of a meeting with United States President Joe Biden this month.

Shots for the general populace are not likely to be available until the late summer or even winter, too late to stem a resurgence of cases that appears to be focused on people in their 30s and 40s, according to Haruka Sakamoto, a physician and researcher at Keio University in Tokyo.

"The currently available vaccination cannot prevent the fourth wave of the pandemic," she said. "I think the younger generation is now going to be more greatly affected compared to the previous waves."