While the number of reported flu cases is down nationwide, a second wave of the illness is starting to spread.
According to the CDC's weekly surveillance report ending March 17, the number of "Influenza B" cases are now being reported more often than the A-strain. During that week, nearly 58 percent of all lab-confirmed cases were caused by the B-strain, according to the report.
Overall, "Influenza A" cases have dominated the flu season up until this point, the CDC noted.
CDC spokesperson Kristen Nordlund explained to CNN that parents with younger children should continue their vigilance.
"We know that illness associated with influenza B can be just as severe as illness associated with influenza A," Nordlund told CNN. "We also know that influenza B tends to be more severe for younger children."
She added that this second wave of B-cases is not unexpected, but it's not yet known what this flu wave will look like.
Since October, 26,694 people have been hospitalized with flu-related symptoms, with nearly 78 percent of those hospitalizations related to the influenza A virus, according to the CDC.
Dr. John Lynch said both strands are keeping Harborview Medical Center in Seattle busy this season.
“We’re seeing just as many flu cases in the ED (Emergency Department) at Harborview Medical Center as we did in the peak season,” said Dr. Lynch. The peak of the season was in January, he added.
“This year influenza B is percolating throughout the entire season,” said Dr. Lynch. “And that’s really important because influenza B is just as dangerous to many people.”
Dr. Lynch said even though this season’s vaccine is only 25 percent effective against Influenza A, the vaccine is more effective versus Influenza B – 43 percent. Either way, Dr. Lynch said it’s still the best option, even late in the season.
“There’s still time to get a flu vaccine. It takes about two weeks to work and it’s a little bit better for influenza B,” he said.
