Last season's flu shot was not badly made. It was made too early. Every winter, experts pick the strains for shots that will not go into anyone's arm until fall. For last season, the U.S. picks were made in March 2025. The H3N2 virus that drove the 2025-26 season, a variant called subclade K, was not identified until June, months after the decision had been locked.
It spread fast. About 93 percent of the H3N2 samples analyzed by the Centers for Disease Control and Prevention last season turned out to be subclade K, and flu hospitalizations reached the third-highest rate since the 2010-11 season. For children under 18, it was the second-highest.
That is what makes this year different. According to CDC, all three components of the 2026-27 vaccine were updated, including a change to protect against subclade K. Last year, only the H3N2 component changed.
CDC recommends getting the shot in September or October and advises most adults against July or August, because protection fades over the course of a long season. If you have not gone yet, you are not late. Flu activity usually peaks between December and February.
Antibodies take about two weeks to build. A shot by mid-November is working by Thanksgiving.
Rick Good spent ten years in the newspaper business, including with The News & Observer (Raleigh, NC) and The Greenville News (Greenville, SC). He co-wrote, with Melinda Coleman, Rutledge to Riley: Governors of South Carolina, 1776–Present (Published by The Greenville News), and is the author of Mind Games Trivia #1 (Amazon). He has recently spent 15 years creating original trivia content through Sounds Good Mobile Entertainment and continues that with his new company, SGME Software. He edits The Smart Reader’s money, real estate, and business coverage.
