Modern flu vaccines have an average efficacy of just 40 percent, and they must be revamped each year. How can we make vaccines that are “universal” — both broadly-protective and highly potent?
A universal flu vaccine may seem elusive, but consider that in the 1920s, many doctors believed curing bacterial infections was impossible. There was, as Thomas Hager writes in The Demon Under the Microscope, a sense that "medicine had reached its limits" — a collective resignation to the belief that infectious diseases would continue to claim lives unchecked. Scientists at the time knew that dozens of different bacteria could cause disease and couldn’t imagine how a small number of drugs could possibly combat them all. Influenza and pneumonia alone caused nearly 30,000 deaths amongst U.S. Army soldiers during World War I, comprising more than half of the 52,000 non-combat deaths recorded.
Viruses mutate rapidly, and influenza’s constant genetic shifts make it hard for vaccines to keep up. The strains used for each year’s vaccine must be predicted a full 6-8 months in advance to give vaccine manufacturers time to ramp up production ahead of the next flu season. But it’s difficult to make accurate predictions so early when viruses mutate every day.