Japan started administering COVID-19 booster shots on Wednesday to individuals who received their second shot at least eight months ago amid growing concerns about the spread of a new coronavirus variant.

Third doses of the vaccine developed by Pfizer Inc. and BioNTech SE were provided to health care professionals across the country, with the elderly and others expected to receive their booster shots from January to prevent the spread of infections and severe symptoms.

A nurse (R) receives her COVID-19 booster shot in Hachioji, Tokyo, on Dec. 1, 2021. (Kyodo)

The government decided to administer booster shots after vaccine-induced immunity against infection was found to wane over time.

Although it remains unclear how effective the booster shots will be against the new coronavirus variant, Omicron, Prime Minister Fumio Kishida has decided Japan will join other countries in administering the booster shots as scheduled.

The Omicron variant, designated as a "variant of concern" by the World Health Organization, was confirmed in Japan for the first time on Tuesday, with a second case reported Wednesday.

Under the current policy in Japan, individuals aged 18 or older will be eligible for a booster shot and those at higher risk of developing severe symptoms, such as the elderly, or those working in high-risk professions will be especially encouraged to get a third shot.

In the meantime, first and second shots will continue to be administered to unvaccinated people in the country.

Toshio Nakagawa, president of the Japan Medical Association, said at a press conference that amid fears of the Omicron variant spreading rapidly, the government should consider bringing forward booster shots.

But he also indicated it would be difficult for all municipalities to move up the schedule at the same time. "I want (the government) to increase the transparency of the vaccine supply schedule so that people will not be confused."

The Pfizer vaccine is the only one to receive approval so far as a booster, the government said, though it added the booster vaccine can be a different brand from the previous two shots administered.

Japan has inoculated over 75 percent of its population with two COVID-19 shots, according to the government, while new coronavirus cases have sharply decreased with only 132 new cases reported across the country on Tuesday.

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