Local governments will be allowed to administer mix-and-match COVID-19 vaccine booster shots six months after a second dose — instead of the initially proposed eight months — now that studies have shown the vaccines' effectiveness against infection wanes by around 50% over the period of half a year.

A health ministry panel on Monday, however, kept unchanged its standard timeline for an eight-month interval between the second and third shots, putting it in line with the practice in many European nations, in order to give time for preparation. But municipalities can give the booster shot at the six-month point if they deem it necessary, the panel said.

The shortened timeline for booster shots came after a study by Yukio Ohsawa, a professor at the the University of Tokyo’s graduate school of engineering, showed that failing to accelerate the rollout of boosters may lead to a wave of infections that could far surpass that of the fifth wave over the summer, with daily cases in Tokyo alone potentially topping 10,000. Daily cases in Tokyo reached a record 5,908 on Aug. 13.