Seasonal-flu vaccines can prevent millions of infections even if they don’t closely match the strains of virus in circulation.
Flu vaccines are reformulated each year in an attempt to keep up with the fast-evolving influenza virus. The 2017–18 vaccine was a particularly poor match to circulating flu strains, and early evidence suggests that this led to a spike in hospitalizations and deaths.
Burton Singer at the University of Florida in Gainesville and his colleagues developed a model to predict the impact of low-efficacy flu vaccines. They found that if 43% of US residents received a vaccine that protected only 20% of recipients, it could still avert some 21 million infections, nearly 130,000 hospitalizations and almost 62,000 deaths.
Vaccinating large numbers of school-age children achieves the most benefit from low-efficacy vaccines. But the model suggested that elderly individuals should also be a priority when the vaccine is particularly ineffective.