The Hong Kong Flu outbreak appeared on 13 July 1968. By the end of July 1968, it was a full on pandemic in Singapore and in Hong Kong.This flu was also thought to have originate in China, and perhaps it did. This is unconfirmed.
That said, while there was a deadly war raging in Southeast Asia, the Hing Kong Flu killed one million people.
When it showed up in the United States brought here by returning troops and eventually locked down and killed.