Japan's health ministry is planning to move ahead with a formal approval of the coronavirus vaccine developed by U.S. pharmaceutical giant Pfizer Inc. on Sunday, when the first batch of doses is scheduled to arrive in the country, sources familiar with the matter said Thursday.

The Health, Labor and Welfare Ministry had intended to approve the Pfizer COVID-19 vaccine on Monday. With an acceleration of its administrative procedures, the government is considering starting vaccinations on Wednesday for around 20,000 doctors and nurses who have consented to receive the shots, the sources said.

Photo taken Jan. 22, 2021, shows U.S. pharmaceutical giant Pfizer Inc.'s production site in Puurs, Belgium. The plant manufactures vaccines for the novel coronavirus, part of which will be exported to Japan. (Kyodo) ==Kyodo

Ahead of the formal approval, a health ministry panel is expected to hold a meeting on Friday night to discuss whether Japan should go ahead with the Pfizer vaccine to deal with the pandemic. It is highly likely that the panel will give the green light, considering that Pfizer's vaccine has already been administered in several countries including the United States.

The roughly 20,000 doctors and nurses from 100 hospitals across the country are set to participate in a study aiming to track potential symptoms and the frequency with which the symptoms occur, regardless of whether the vaccine is the cause.

After the arrival from Belgium of the first batch of the vaccine, jointly developed by Pfizer and its German partner BioNTech SE, it remains unclear when and in what amount Japan can secure further quantities of the vaccine due to tightening EU export controls of products developed in the bloc.

Japan aims to secure the necessary doses of the Pfizer vaccine through negotiations with the European Union.

A nurse prepares a Pfizer BioNTech COVID-19 vaccine in Paris on Jan. 18, 2021. (Getty/Kyodo)

The government has agreements in place to receive enough vaccine doses for 157 million people, more than enough to cover Japan's population of 126 million. Of the total number, 72 million doses are to come from Pfizer. The remainder will be provided by AstraZeneca Plc and Moderna Inc.

About 20,000 ultra-cold freezers are slated to be set up at medical facilities across Japan to store the Pfizer vaccine, which was 95 percent effective in clinical trials. The AstraZeneca vaccine can be stored at 2 to 8 C, making it easier to handle, but is only around 70 percent effective.