On the domestic front, travelers arriving in the U.S. from the U.K. are now required to show proof of a negative COVID-19 test under new rules issued by CDC on Christmas day.

More than 40 other nations have gone even farther, blocking travelers from Britain entirely. Despite such measures, the new strain has already been detected in mainland Europe, Israel, Canada and Japan, among other places.

In response Japan is banning nearly all foreigners (the declaration lists nationals from 152 countries as personae non gratae at least until February) and is imposing new restrictions on Japanese citizens returning from any country that’s reported cases of the U.K. variant. The new Japanese rules also apply to places where the South African strain is circulating.

A surge in cases and concerns over the more highly transmissible forms of the virus prompted Israel to go into its third lockdown on Sunday.