Nearly 400 people in Japan have been infected with a new variant of the novel coronavirus different from those found in Britain, South Africa and Brazil, Japan's National Institute of Infectious Diseases said Tuesday.

While differing from those discovered earlier in the three countries, the new strain found in Japan shares some commonality with those from South Africa and Brazil, the institute said. It is suspected that the commonality may cause more reinfection and that current vaccines may be less effective against it.

Supplied photo taken on Feb. 27, 2020 shows PCR tests being carried out at a laboratory at Japan's National Institute of Infectious Diseases. (Photo courtesy of Japan's National Institute of Infectious Diseases) (Kyodo)   

The institute found that as of Wednesday last week the newly discovered variant had infected 394 people at home, mostly in Japan's Kanto region centering on Tokyo, while two were found infected with the variant during quarantine.

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"We do not think that this variant is becoming more mainstream, but will continue to strive to gain understanding of the situation," said Tomoya Saito, head of the institute's Center for Emergency Preparedness and Response.

Supplied electron micrograph shows a variant strain of the novel coronavirus originating from Britain. (Photo courtesy of Japan's National Institute of Infectious Diseases)(Kyodo)

The new viral strain is thought to have come from overseas but details are still unknown, he said.

The institute also said it is better to prioritize responses against the British variant, which is considered more contagious.