Health officials in Japan have confirmed a third coronavirus variant that is reported to be separate from the strains that were first documented in the U.K. and South Africa.

Makoto Shimoaraiso, an official with Japan’s Cabinet Secretariat and Office for COVID-19 Preparedness and Response, said Tuesday that the strain might have originated outside of Japan, given that the cases were documented in an airport, according to The New York Times.

The variant was detected in four people who traveled to Japan from Brazil.

It is not clear whether the third strain is more transmissible or causes more severe cases of COVID-19. The other two mutations first found in the U.K. and South Africa are believed to be more contagious than the original strain.

Japan last week declared a state of emergency in the greater Tokyo area, with Japanese Prime Minister Yoshihide Suga saying additional measures were needed to address the “increasingly troubling” third wave of infections.

The leader of the World Health Organization on Monday said that increased opportunities for transmission can result in more mutations.

“The more the virus spreads, the higher the chance of new changes to the virus. Most notably, transmissibility of some variants of the virus appears to be increasing,” WHO Director General Tedros Adhanom Ghebreyesus said.