Japan plans to start inoculating elderly people only after the coronavirus vaccinations for frontline health workers have been administered, possibly delaying the initially anticipated start date for seniors in April, a senior government official said Monday.

The move aims to ensure a stable supply of Pfizer Inc.'s vaccine, which was formally approved by the health ministry on Sunday, the official said. Around 3.7 million health workers are to begin receiving the vaccine in March, followed by 36 million people aged 65 and older from April 1 at the earliest.

Participants check the injection procedure for vaccinating medical workers against the novel coronavirus during a training session at Fujita Health University in Aichi Prefecture on Feb. 12, 2021. (Kyodo)

But, according to another government official, it is uncertain when Japan can receive subsequent shipments and how much, following the European Union's tightening of export controls on vaccines. Pfizer is also likely to delay its plan to increase production capacity from March.

But once a sufficient supply of vaccines has been secured, inoculations could still take place simultaneously for front-liners and the elderly.

After a total of 3 million doses are administered to the general public, Japan will survey the potential side effects caused by various coronavirus vaccines, the Ministry of Health, Labor and Welfare said Monday.

The ministry will invite participants to respond to its survey after the inoculation for the elderly people and plans to track common side effects such as fever and fatigue among three different vaccines, including Pfizer's.

Around 10,000 to 20,000 health care workers are set to begin receiving their first dose of the Pfizer vaccine on Feb. 17. The government will collect and periodically release details about all side effects experienced, regardless of whether the vaccine is the cause.

It will also provide information on the safety of the vaccines garnered from the survey after inoculations begin for the general public.

The survey is expected to cover around 500,000 people per single dose of each version of the vaccine. A total of 3 million doses will be necessary if the government includes doses by pharmaceuticals AstraZeneca Plc and Moderna Inc., alongside Pfizer.