U.S. health officials say the worst of this season’s unusually strong flu outbreak is over. 

In its weekly report Friday, the U.S. Centers for Disease Control and Prevention (CDC) said the flu peaked in early February and is now on the decline. However, health officials say that while the worst has passed, the flu season is not yet over, and will likely continue for weeks. 

The agency said reports of the influenza virus remained widespread in 45 states. 

The Midwestern state of Indiana reported Friday that it recorded 244 flu-related deaths this season. Seventy-five percent of the deaths were in people age 65 and older. Nine of the deaths were in people under the age of 25. 

Nationwide, health officials say 114 children have died from the flu this season. 

Flu season usually begins in earnest in late December and peaks around February. This season, the virus was widespread in many states by early December last year.

Health officials have said it is not clear why the flu has been so severe this year.

The dominant strain this season, influenza A (H3N2), is especially strong and tends to lead to more hospitalizations and deaths than other more common strains. Still, last year’s outbreak of influenza A was not as severe as this year.

Experts say that flu seasons are notoriously hard to predict.

Also contributing to the difficulties this year was the fact that the vaccine did not work very well and health officials say they are trying to figure out why it did so poorly.

Flu is a contagious respiratory illness that causes such symptoms as fever, cough, muscle aches, headaches and fatigue. Most people who get the flu get better within a week or two. However, some people develop serious complications caused by a viral infection of the nasal passages and throat and lungs.