TOKYO - Japan began on Wednesday to administer COVID-19 booster injections to people who finished the full two shots at least eight months ago amid increasing concerns over the new Omicron variant of the COVID-19, the government said.

The third dose of the vaccine developed by Pfizer and BioNTech SE were provided to health care professionals across the country. The elderly and others are expected to receive booster injections from January.

Although the effectiveness of the booster shots remains unknown against the new Omicron variant, Prime Minister Fumio Kishida has decided that Japan will administer the booster shots as scheduled, as vaccine-induced immunity against infection was confirmed to weaken over time.

Individuals aged 18 or above will be eligible for the third injection, under Japan's current policy, and especially those who are at higher risk of severe symptoms such as the elderly or those engaged in high-risk occupations will be especially encouraged to get a booster shot.

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

The government approved the Pfizer vaccine as the only vaccine to be used for the booster injection so far. It added that the booster vaccine can be a different brand from the previous two injections.

The rate of population in Japan inoculated with two COVID-19 vaccine shots stood at over 75 percent, while new COVID-19 infection cases nationwide have sharply declined to only 132 on Tuesday, according to the government data.

The Omicron variant of COVID-19 was first reported last week by South Africa to the World Health Organization, which named the strain as a "variant of concern." Japan confirmed the first case infected with the Omicron variant on Tuesday.