What it means to say the flu vaccine is 'only' 23 percent effective


This flu season, national health authorities made a relatively poor guess of which flu strain would be going around. As a result, the media has endlessly repeated a study finding that this year's flu vaccine is only "23 percent effective." Offhand, you might guess that this means only 23 percent of vaccinated people are protected against the flu — or maybe you could somehow get one-fourth of a case of the flu?
Not quite. It turns out this definition is quite complicated, and isn't even a measurement of the general population, but instead of people with acute respiratory infections. Aaron Carroll carefully explains the details below, but the bottom line is that even when the flu shot isn't a great match, it's still worth getting. —Ryan Cooper
A free daily email with the biggest news stories of the day – and the best features from TheWeek.com
Subscribe to The Week
Escape your echo chamber. Get the facts behind the news, plus analysis from multiple perspectives.

Sign up for The Week's Free Newsletters
From our morning news briefing to a weekly Good News Newsletter, get the best of The Week delivered directly to your inbox.
From our morning news briefing to a weekly Good News Newsletter, get the best of The Week delivered directly to your inbox.
Ryan Cooper is a national correspondent at TheWeek.com. His work has appeared in the Washington Monthly, The New Republic, and the Washington Post.
-
RFK Jr. shuts down mRNA vaccine funding at agency
Speed Read The decision canceled or modified 22 projects, primarily for work on vaccines and therapeutics for respiratory viruses
-
Measles cases surge to 33-year high
Speed Read The infection was declared eliminated from the US in 2000 but has seen a resurgence amid vaccine hesitancy
-
Kennedy's vaccine panel signals skepticism, change
Speed Read RFK Jr.'s new vaccine advisory board intends to make changes to the decades-old US immunization system
-
Kennedy ousts entire CDC vaccine advisory panel
speed read Health Secretary RFK Jr. is a longtime anti-vaccine activist who has criticized the panel of experts
-
RFK Jr. scraps Covid shots for pregnant women, kids
Speed Read The Health Secretary announced a policy change without informing CDC officials
-
New FDA chiefs limit Covid-19 shots to elderly, sick
speed read The FDA set stricter approval standards for booster shots
-
US overdose deaths plunged 27% last year
speed read Drug overdose still 'remains the leading cause of death for Americans aged 18-44,' said the CDC
-
Trump seeks to cut drug prices via executive order
speed read The president's order tells pharmaceutical companies to lower prescription drug prices, but it will likely be thrown out by the courts