Forty-six states are reporting widespread influenza activity, and the flu's reach is likely to expand as the season progresses, according to the Centers for Disease Control.
Only California, Arizona and Alaska report regional flu activity, while Hawaii and the District of Columbia report local activity. California recently reported its first influenza death for the 2014-2015 season and the state's director of the department of public health said that flu activity is beginning to increase statewide.
Different variations of the flu circulate every year, but for the first time since the 2012-2013 season, the H3N2 influenza A virus is the predominant strain, accounting for 95 percent of all influenza cases reported to the CDC.
"We're looking at a season that is shaping up to be about as severe as that season," said Dr. Michael Jhung, medical officer with the influenza division at the CDC. "Of course, we won't know until the end of this current season, how bad this season is."
Flu cases begin to decrease in March and April, although sporadic cases can still be seen in May, he added.
Several studies have been done that suggest a season pattern with influenza, including this 2010 NOAA study, which looked at the effects of weather on the illness, but a definitive answer remains unclear.
Another reason for the rapid spread of the flu may include people spending more time indoors during the winter months where the spreading of illness can thrive.
"It's complicated, there are likely many factors involved," Jhung said, citing the traditional school season when many people are congregated in classrooms as one factor.
"That's one reason that flu activity may increase in the seasonal pattern that we see in the United States," he said. "In other words, it tends to spike in the winter months and decline dramatically in the summer months."
Presently, the CDC is not researching seasonality and any connections to the flu, Jhung said.
"There is still some hypotheses as to why there is a flu season every year, but it's certainly not something that has been proven or shown," Jhung said. "There hasn't been a smoking gun, so to speak, to say why there's a flu season and why it happens in the winter months."
Dr. Jeffrey Shaman, an assistant professor in the department of Environmental Health Sciences at Columbia University, created a flu forecast that predicts the spread of the influenza virus up to seven weeks in advance. Their first real-time forecasts were performed during the 2012-2013 season.
As previously reported on AccuWeather.com, Shaman's model uses some of the basic principles used for weather forecasting and examined the notion that influenza outbreaks are specific to each region and associated with absolute humidity levels.
This past June, Shaman and his team of researchers were awarded first prize in the CDC's "Predict the Influenza Season Challenge," a contest launched in November 2013 to "promote innovation in flu activity modeling and prediction," according to the CDC. His group's current forecasts can be seen here.
"We seem to be past the peak at least with respect to H3N2 in much of the South and Midwest," Shaman said. "Some areas in the Northeast and West still may have another week or two of increasing incidence."
After that, the model predicts a decline but doesn't preclude the outbreak of another flu type, Shaman said. He added that some areas have been having substantive influenza B activity coincident with the H3N2, so they may experience a second smaller peak in the coming weeks.
On Thursday, the CDC said that the flu vaccine is only 23 percent effective this season among people of all ages. The similarity between the flu virus used in the vaccine production and the actual virus circulating is typically one factor in determining success.
"H3N2 viruses have been predominant so far this season, but about 70 percent of them have been different or have 'drifted' from the H3N2 vaccine virus. This likely accounts for the reduced [vaccine effectiveness]," the CDC said.
Despite the reduced effectiveness, the CDC still recommends that everyone six months and older receive a flu shot because the vaccine can still prevent against other forms of influenza.
Those who have the highest risk for flu are very young children (under two years old), adults ages 65 and older, or those who have an underlying medical condition, according to Jhung.
The CDC also suggests taking daily preventive actions to stop the spread of germs to help fight the flu.
2. Stay home when you are sick.
3. Cover your mouth and nose with a tissue when coughing or sneezing.
4. Wash your hands often.
5. Avoid touching your eyes, nose or mouth.