Have you ever had the flu? Most people recover from it pretty fast. However, the flu still kills thousands of children and adults each year. This makes it a big health problem across the world. The best way we can prevent flu infection is by getting vaccinated. The problem with the flu vaccine is that in some years it doesn’t work as well as others. For example, in 2017-2018 the flu vaccine was less effective in preventing infection among vaccinated people compared to previous years.
We wanted to study the impact of less effective vaccines in preventing flu-related infections, hospitalizations, and deaths. We found that even when the flu vaccines don’t work well, they prevent a large number of people from getting infected or hospitalized and save thousands of lives. This effect is called herd immunity. We also learned that when vaccines are less effective, it is most important for school-age children, young adults, and the elderly to be vaccinated.