By Stephanie Stahl

PHILADELPHIA (CBS) — It’s been a bad flu season for kids, but the Centers for Disease Control and Prevention said the vaccine is working OK, so far. The flu vaccine is based on an educated guess of what strains will be circulating because it’s made before the flu season starts.

That’s why there are variations each year, but on Thursday, we got the first official evaluation of this year’s batch.

The flu vaccine doesn’t offer perfect protection — it never does — but the latest CDC report says it is providing substantial protective benefit, especially for children.

Flu vaccines are reducing doctor visits related to flu by 45% overall and 55% in children, according to preliminary estimates.

“This season has been more severe in children than in previous seasons,” CDC epidemiologist Brendan Flannery said. “And that may have to do with the type of influenza that is circulating. Influenza B can be more severe in children.”

Flu vaccine effectiveness typically ranges from 40% to 60%.

This season got off to an early and unusual start with flu B viruses dominating and now a second wave of flu A H1N1 is hitting.

So far, the vaccine appears to be less effective against H1N1 for younger adults.

In the U.S., there have been at least 26 million illnesses, 250,000 hospitalizations and 14,000 deaths from flu this season.

“Right now, the map of the U.S. looks pretty red and that means a lot of flu activity. Most of the areas have the highest flu activity we see during the season,” Flannery explained.

Since we’re still in the middle of prime flu season, experts say it’s not too late for a flu shot, which offers the best protection, along with constant handwashing.

People are being reminded to cover your cough and sneeze and stay home when you are sick to avoid spreading the virus.

Experts say the overall effectiveness of the flu vaccine could change because other strains could pop up.

In terms of the two strains circulating this season, they’re not as dangerous to the elderly.

Stephanie Stahl