The flu shot is 36 percent effective in adults this winter, while getting young children vaccinated for the flu can make them 59 percent less likely to become infected and have to go to the doctor, federal health officials said Thursday.
The number of children who died from the flu climbed to 63 this past week, and additional deaths are expected to be announced soon. Three out of four children who died had not been vaccinated.
"We continue to recommend parents get their children vaccinated even though it's fairly late in the season," said Anne Schuchat, acting director at the Centers for Disease Control and Prevention.
The latest estimates come as officials say that this flu season has hosted certain virus strains that tend to cause more illness than others. The trend in higher-than-usual hospitalizations and illness is expected to continue for several weeks.
"This season has been particularly hard in that it seemed to hit everywhere in the United States at once," Schuchat said.
While the strains that are circulating are the same ones that scientists had projected when they were developing the vaccine, officials said they believe one of the reasons it lacks effectiveness in adults is because of how it was developed, by being grown in eggs. Doing that may have caused the virus to mutate or change in ways that evade the vaccine, Schuchat explained.
"The problem is that the vaccine isn't working as well as we had hoped in general, although in children it appears to be working as well as expected," she said.
Government agencies are working with the private sector to see whether they can come up with better ways to produce effective vaccines, she continued.
Health and Human Services Secretary Alex Azar stressed that though people who have the vaccine can still get infected, the illness will be less severe. He also pointed out that being vaccinated makes people less likely to pass on the illness to vulnerable populations, such as children and older adults.
Surgeon General Jerome Adams urged the public to go to a general care provider if they believe they have been infected, but to go to the emergency department if they have symptoms like a high fever, rapid heartbeat, and confusion.