Updated at 9:23 a.m. on Friday, June 28, 2019, with more information.
ATLANTA — The flu vaccine turned out to be a big disappointment again.
The vaccine didn't work against a flu bug that popped up halfway through the past flu season, dragging down overall effectiveness to 29%, the U.S. Centers for Disease Control and Prevention reported Thursday.
The flu shot was working well early in the season with effectiveness put at 47% in February. But it was virtually worthless during a second wave driven by a tougher strain, at just 9%.
There was "no significant protection" against that strain, said the CDC's Brendan Flannery.
Flu vaccines are made each year to protect against three or four different kinds of flu virus. The ingredients are based on predictions of what strains will make people sick the following winter.
This season's shot turned out to be a mismatch against the bug that showed up late.
That pushed down the overall effectiveness to one of the lowest in recent years. Since 2011, the only season with a lower estimate was the winter of 2014-2015, when effectiveness was 19%. A mismatch was also blamed then.
Flu shots are recommended for virtually all Americans age 6 months or older. Officials say the vaccine is still worthwhile since it works against some strains, and it likely prevented 40,000 to 90,000 hospitalizations over the winter flu season.
The CDC bases vaccine effectiveness on preventing cases bad enough to send someone to the doctor.
Kayla Johnson, a nurse practitioner at CHI Memorial Convenient Care- Atrium, told the Times Free Press in September that convincing people to get a flu shot is always a challenge because the vaccine works better some years than others.
"One of patients' biggest objections to getting the flu vaccine is concern that it won't work," Johnson said at the time. "I always stress to patients that the benefits of getting the flu vaccine far outweigh the risks of not getting the flu vaccine."