Vaccination can prevent three of every four flu infections, even when the vaccines are imperfectly tailored to block the common wintertime pathogens, a new study shows. That finding is reassuring, researchers say, because it's difficult to anticipate how the flu virus will evolve each year during the time from the start of vaccine manufacture to deployment.
The flu reinvents itself from year to year through a process in which previously rare variants of the virus supplant once-dominant ones. Since a vaccine trains the immune system to spot viruses by their unique surface proteins, a vaccine may work poorly if an unexpected variant dominates the flu season.
Past research has shown that injected and inhaled vaccines perform comparably, with efficacy as high as 90 percent, when the vaccine is on the mark. But in about 3 years out of every 10, designers guess incorrectly which variants of flu will predominate, says Arnold Monto of the University of Michigan in Ann Arbor.