Why Is It So Hard to Make a Universal Flu Vaccine?
Your annual flu shot protects you from some types of flu, usually the ones that got people sick the year before. But if a new strain of flu shows up, the shot may not work for it. That's why a holy grail of medicine is to create a universal flu vaccine. A universal flu vaccine can't come soon enough, especially for particularly vulnerable populations, such as children, the elderly and the immune-compromised. More than 650,000 people around the world die of seasonal influenza every year, according to the World Health Organization. Seasonal flu also costs the U.S. healthcare system and society in general, a pretty penny, about $11.2 billion in 2018.
Source: How Stuff Works