Testing has already begun to determine whether the Pfizer vaccine protects against a mutant strain of COVID-19 that first appeared in Africa and has already made its way to East Asia and Europe, the Financial Times reported Friday.

German firm BioNTech, which developed the jab in concert with the American pharma giant, told the paper that it would know in two weeks whether the inoculation shields against the latest variant, which has prompted multiple nations to shut their borders to travelers from southern Africa. Authorities have already detected the super-mutated virus—now called Omicron—in South Africa, Botswana, Hong Kong, and Belgium.

A spokesman for BioNTech noted that this line of the pandemic pathogen “differs significantly” from its predecessors due to the changes in its spike protein, which the virus uses to hack into human cells—and which the vaccines help neutralize. The company added that it could take six weeks to modify the vaccine if necessary, and 100 days to ship the updated shots.