Bacterial pneumonia is the most important and serious complications of the flu.
Doctors say it can affect, even cause death, in otherwise healthy children and adults.
"Years where we see H3N2 as the predominant strain, we typically see more deaths, more hospitalizations that year and this is one of those years, unfortunately," said Dr. Edward Dominguez, infectious disease doctor at Methodist Dallas.
H3N2 is the most aggressive strain of the flu, according Dr. Dominguez, who also worked at the Baylor College of Medicine's Influenza Research Center in Houston.
He said historically, vaccinations have only ever been 30 percent effective against the H3N2 strain.
It can sicken, even lead to bacterial infections, in the healthiest person.
"The most important thing it does is it takes away the lining of the lungs and the airways. By doing that, the mechanism that we bring up bacteria, that we normally bring in during our daily lives, Is gone, so the bacteria, after the influenza may be improving, are beginning to grow and stay in the lungs."
Then, even if your flu seems to be going away, a second infection kicks in.
"The bacteria infection occurs because your lungs can't clear the bacteria. When they build up to critical mass, they have access to the bloodstream. That causes sepsis, and then unfortunately, literally within 24 to 48 hours, in some people, you can see this play out in a very catastrophic way."
He says the scenario is unlikely in many people, but this particular flu season, he and experts at the CDC are warning against taking your chances and getting treated for the flu right away.
Many doctors are now prescribing the anti-viral Tamiflu, even before a patient takes a flu test.
Tamiflu is most effective when you take at the beginning of your illness, but it's suggested providers prescribe it beyond the recommended 48-hour window.
"We can only recommend the medication the way that it was studied and improved, but that doesn't mean that the medication isn't valuable after 48 hours. In fact, it really is! And many of us have continued to use it when people come in on day three, four, five of their illness."
He also says some immunity from this year's vaccine is still better than no immunity and can help protect you against secondary infections.
Fever, which is a hundred degrees or higher, is the most common flu symptom. Doctors say call for medical guidance if you think you have the flu.
Bacterial pneumonia is the most common secondary infection and symptoms are chest pain, severe chills and chest congestion.