Japan's Covid-19 case numbers have plummeted to the lowest in nearly a year just as other parts of Asia are struggling with surging infections, leaving health experts perplexed and raising concern of a winter rebound, according to Reuters.

New daily cases in Tokyo dropped to 87 on Monday, the lowest tally since Nov 2 last year, and a precipitous decline from more than 5,000 a day in an August wave that hammered the capital's medical infrastructure.

“Without the elimination of the virus, we will continue to see spikes until 85 per cent of the population is immune to the dominant strain,” said Jason Tetro, a Canada-based infectious disease expert.