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Molly Riley, Associated Press
Dr. Anne Schuchat, Director of the National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, testifies before the House Energy and Commerce subcommittee hearing looking into the effectiveness of vaccines in the wake of a measles outbreak and the exceptionally severe flu season, in Washington, Tuesday, February 3, 2015. Federal health officials faced tough questioning Tuesday about why this year's flu vaccine isn't giving good protection against the winter menace.

WASHINGTON — Federal health officials faced tough questioning Tuesday about why this year's flu vaccine isn't giving good protection against the winter menace.

This is a particularly bad flu season, and one reason is that the most common flu strain isn't a good match to this year's vaccine. Lawmakers on Tuesday asked why the Centers for Disease Control and Prevention didn't act months ago when concerns first arose to create a better-matched vaccine.

CDC immunization chief Dr. Anne Schuchat says it wasn't possible to change course. While CDC first noticed a slight change in that strain last March, by the time the shift had become common in September, it was too late.

"We're all frustrated," said Rep. Tim Murphy, R-Pa., who called the House Energy and Commerce oversight subcommittee hearing to examine ways to improve the flu vaccine production process.

This year's flu vaccine is proving to be about 23 percent effective, far less than the usual 50 percent to 60 percent. With far more than usual hospitalizations among the elderly, it is a severe flu season. On average about 24,000 American die from flu each year.

At the same time, lawmakers reacted to headlines about the measles outbreak, which has sickened more than 100, by urging that kids be vaccinated against the highly contagious disease.

One by one, federal health officials expressed their strong support for the measles vaccine, calling it very effective and safe.

"Vaccines save lives and are the best way for parents to protect their children from vaccine-preventable diseases," Schuchat said.

Dr. Anthony Fauci of the National Institutes of Health said the decision to vaccinate against measles "is really a slam-dunk."