An Extremely Thorough Guide to This Year’s Flu Season

Answers to the most pressing questions about the influenza virus, flu vaccine, and everything else you should know

Last year’s flu season was a doozy. According to the Centers for Disease Control and Prevention (CDC), the 2018–19 flu season lasted 21 weeks — making it the longest in a decade. Already this year, the flu has claimed at least one life — a 4-year-old living in California — which has led some public health officials to state that this year’s season may, too, be a rough one.

“The flu is hard to forecast, but already we’ve been seeing scattered reports of flu,” says Stephen Morse, a flu expert and professor of epidemiology at Columbia University’s Mailman School of Public Health. That could mean that this year’s season will be bad, he says, or it could mean that the season will peak early and quickly burn itself out. Whether the 2019–20 flu season turns out to be merciless or mild, Morse says the early emergence of the flu should lead people to get their flu shot sooner rather than later — and preferably by the end of October.

While the CDC’s annual influenza stats are approximations, the flu infects some 30 million or more Americans in a typical year. In bad years, such as the 2017–18 season, the flu infected nearly…