Japan has started vaccinating its elderly citizens against COVID-19, as Tokyo introduces a slew of new restrictions to avert a fourth wave of the pandemic.

Just about 120 sites in Japan opened Monday to administer the first dose of the two-shot Pfizer vaccine to people aged 65 and up. Officials anticipate that approximately 100 million doses of the Pfizer vaccine will arrive by the end of June, enough to inoculate Japan's 36 million elderly residents.

The vaccinations come amid increasing concern about a resurgence of infections in some areas, including Tokyo and the prefectures of Osaka and Kyoto, following the country's lifting of a second state of emergency over the virus last month.

The Japanese government has named prefectures with an increase in cases as requiring tough measures to monitor its spread but has stopped short of declaring a third state of emergency, ostensibly to avoid complicating attempts to host the postponed Tokyo Olympics and Paralympics this summer.

The Olympic torch relay started in Japan several days after the second state of emergency ended.

With the medical system under growing pressure as infections resurface, there is fear that doctors and nurses may be unable to keep up with the vaccination schedule.

According to a Kyodo News tally, local governments in at least 39 of the country's 47 prefectures planned to begin vaccinating older citizens Monday at clinics as well as facilities such as public halls and gymnasiums.

Vaccine deliveries to prefectures began last week with 100 boxes, each of which included enough vaccines for two shots for 500 people. Except for the more populous Tokyo, Kanagawa, and Osaka prefectures, which each received four boxes, each prefecture received two boxes.

The rollout is expected to pick up speed in the final week of April when all 1,741 municipalities in the country will have received one package.

Japan began its vaccination campaign in mid-February, beginning with approximately 4.8 million health care workers.