U.S. health officials are officially calling the rise of flu cases an "epidemic" as a strand of H1N1 -- the same type of strain as the so-called "swine flu" that spread nationwide in 2009 -- continues to affect two crucial groups: pregnant women and people under 40 years old.

One day after Brevard County health officials said a woman died from the flu virus just weeks after giving birth to a newborn baby, health centers around Central Florida are reporting more influenza cases, and the latest ones are more severe.

Alex Bryan was the second Brevard County woman to die from the flu in 2014. Doctors said she contracted H1N1 and did not get a flu shot.

Weeks earlier, a woman in her 30s also died from the flu in the same Melbourne hospital.

"Our primary concern is pregnant women, because it seems pregnant woman are seeing more complications, and have a higher risk of ending up in intensive care than non-pregnant women" said Dr. Tim Hendrix, with Florida Hospital Centra Care in Winter Park. "Plus, younger adults seem to be more effected by this virus."

Hendrix said the number of cases in Florida has gone from about 100 cases a week in December to 477 cases this week.

"This is the same virus we saw back in 2009–10," Hendrix said. "The pandemic flu, the 'swine flu,' H1N1."

"Older adults are believed to have some immunity to this strain, whereas younger adults don't have any," said Dain Weister, with the Florida Department of Health in Orange County.

Weister said Orange County does not keep track of flu death rates, but Central Florida is seeing more flu cases, and more severe complications, including bacterial infections, which is what killed Bryan.

"What we are urging, and what we are continuing to urge, is to make sure you get the vaccine," said Weister. "You can still get the vaccine, and it will last you this flu season."

Centra Cares around Central Florida have reported about a 90-minute wait time to see a doctor. At the Centra Care on Lee Road in Winter Park, the wait time was about 2 hours.