Harris made the announcement during a meeting with Vietnamese Prime Minister Pham Minh Chinh shortly after she arrived in Hanoi from Singapore.
The U.S. has already donated 5 million doses to the country.
She said the vaccines would start arriving in Vietnam within a day. The vice president has been on a weeklong tour of the region, reassuring U.S. support of Southeast Asia and countering Chinese influence.
In addition to the new vaccine doses, the U.S. will provide $23 million in American Rescue Plan and emergency funding through the Centers for Disease Control and Prevention and the U.S. Agency for International Development to help Vietnam expand distribution and access to vaccines, combat the COVID-19 pandemic and prepare for future disease threats.
The Defense Department is also delivering 77 freezers to store the vaccines throughout the country.
The delta variant has surged through the country, causing record numbers of cases with so many citizens unvaccinated.
Ho Chi Minh City, the nation’s business hub and the epicenter of the most recent outbreak, was forced into a lockdown enforced by armed soldiers on the streets.
"Our relationship has come a long way in a quarter of a century," Harris said in a meeting with Vietnamese President Ngyuen Xuan Phuc.
In the afternoon, Harris will join a health security event with the health ministers from the Association of Southeast Asian Nations group and Papua New Guinea, where she'll speak more about the launch of the CDC center.
Harris’ trip has been overshadowed by the U.S’s frantic efforts to get evacuees out of Afghanistan as the Taliban takes over control of the country.
The Associated Press contributed to this report.