This season the potentially deadly virus is in rare form. Public-health experts are predicting that this year’s flu will be severe for several reasons. Cases are starting up early, which is one indicator of an aggressive virus. Another worry: Australia’s flu season typically augurs that of the U.S., and so far this year, Australia recorded 2½ times as many cases, compared to the same period last year.
What’s more, experts report that the flu vaccine, designed to inoculate hundreds of millions of people, may not be as effective as they’d hoped.
Normally in severe flu seasons like this one, the reasons for the suffering are pretty straightforward. Flu vaccines have long been manufactured in a decades-old process that involves growing the influenza virus in millions of chicken eggs, over a period of about four months. That means flu-shot manufacturers need a head start. Every year in the spring, influenza experts at the World Health Organization (WHO) make their best educated guess, based on the previous year’s flu cases, about which strains of the virus will make the rounds in the coming winter. Sometimes they nail it. But sometimes they don’t—and entirely different strains circulate that make people sick.
The virus can also mutate quickly, so by the time the vaccines are doled out, the bugs people are spreading through sneezes and coughs may be different from the ones you were vaccinated against.