The sixth batch of COVID-19 vaccine developed by U.S. pharmaceutical firm Pfizer Inc. arrived in Japan on Monday as the government continues to inoculate health care workers in the first stage of its vaccination campaign.

The shipment of vaccine bottles providing up to 654,615 doses, with six shots available from each bottle, was delivered to Narita airport near Tokyo from the drugmaker's factory in Belgium.

The central government is set to deliver Monday's shipment along with some other recently arrived bottles to prefectural governments later this week to provide first and second inoculations for up to 117,000 and 292,500 health care workers, respectively.

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Japan is in the midst of inoculating about 4.8 million health care workers and plans to expand the vaccine rollout to the rest of the population, starting off with people aged 65 or older, a group of about 36 million, from April 12.

People with medical conditions such as diabetes and psychiatric disorders will follow.

A total of 553,454 people had received the first shot as of 5 p.m. Friday, according to the health ministry.

The vaccine developed by Pfizer and its German partner BioNTech SE was the first to be approved for use in Japan in February.

Britain's AstraZeneca Plc filed for the approval of its COVID-19 vaccine in early February, followed by U.S. biotechnology company Moderna Inc. earlier this month.

Prime Minister Yoshihide Suga has pledged to secure enough COVID-19 vaccines for Japan's population of 126 million within the first half of 2021.