The government on Monday said it has so far detected more than 20 cases of the Indian variant of COVID-19 in Japan — a rise in the number of cases of the potentially worrisome new strain that some fear could prove more resistant to existing vaccines.

“According to the National Institute of Infectious Diseases, a total of 21 cases were confirmed in the country, of which 20 were found in airport quarantine and one was confirmed among domestic cases,” Chief Cabinet Secretary Katsunobu Kato, the government’s top spokesman, told a news conference Monday.

The government acknowledged for the first time last week that it had detected five cases of the "double mutant" variant, which has the features of two different viral mutations. India has also detected a “triple mutant” variant, and Kato said that the health ministry was looking into the situation.