The emergency grant will enable the countries, all of them in Southeast Asia, Southwest Asia and the Pacific, to vaccinate their populations.
It would be provided through UNICEF, Japan’s Ministry of Foreign Affairs said.
"This emergency grant aid is aimed at delivering vaccines to each and every person in the all corners of developing countries, which will complement the efforts of the Covax Facility," it said. Covax is a global mechanism for developing, manufacturing and procuring Covid-19 vaccines and supplying member countries.
Vietnam began its vaccination campaign on Monday, starting with prioritized categories of people like frontline workers in 13 cities and provinces recently facing coronavirus outbreaks.
It has ordered 30 million doses from British-Swedish firm AstraZeneca, and around 117,600 arrived late last month.
It will receive another 4.1 million AstraZeneca doses through Covax by April.
The coronavirus tally so far in Vietnam is 2,526, with 483 active cases.