In the summer of 1968, a new strain of influenza appeared in Hong Kong. This strain, known as H3N2, spread around the globe and eventually killed an estimated 1 million people. A new study reveals that there are many strains of H3N2 circulating in birds and pigs that are genetically similar to the 1968 strain and have the potential to generate a pandemic if they leap to humans. The researchers also found that current flu vaccines might not offer protection against these strains.