Vietnam recently said it had registered to buy millions of COVID-19 vaccine from Russia after that country’s surprising announcement that it had approved one. The Russian announcement came less than two months after the start of human testing of the vaccine. The vaccine only completed its Phase 2 trials. A Phase 3 trial involving tens of thousands of people is normally required before a vaccine can be approved. After Russia said it had approved a vaccine, the United States, an important partner of Vietnam, expressed disbelief that Russia could have developed a vaccine so quickly. And the World Health Organization (WHO) urged the country to make sure it followed international guidelines in its effort. The WHO says more than 150 programs are currently researching possible vaccines around the world, including those in China, Australia, Britain and the United States. But Vietnam’s long history with Russia might help explain their vaccine deal. Vietnam is one of the last remaining communist nations, which had strong ties to the old Soviet Union.