NHK reports on the matter

The vaccine rollout in Japan is lagging dramatically as the only approved vaccine so far has been Pfizer's vaccine. As of 29 April, just over 995,000 persons (0.8%) have been fully vaccinated in Japan with roughly only 2% of its population having received at least one vaccine dose. Those are rather poor statistics to say the least and does not make for an optimistic narrative that the country could break free of the virus cycle for now.