Why the Vaccinated Still Caught the Flu This Winter

Vaccination has been recommended for decades as the best way to protect yourself against flu, but it’s no silver bullet. The shot’s effectiveness varies from year to year, depending on the closeness of the match between that season’s viruses and the vaccine, which is usually reformulated each year. This winter in North America, its performance has been especially poor, leaving people more vulnerable to a virus that’s caused a spike in hospitalizations and deaths. In Hong Kong, schools are starting their Chinese New Year holiday earlier amid a flu epidemic that has claimed more than 100 lives in the city.

Early findings from Canada indicate a 17 percent effectiveness against the viral strain, known as H3N2, that’s been the main culprit of flu in the U.S. this winter.