Last winter was a calm flu season with relatively few infections.
Dr. Pablo Okhuysen is a professor of infectious diseases at the UT Health Science Center. He says this year the flu started circulating early and heavily across the country. Most of the cases, about 80 percent, are strains of Influenza A.
"This is due to the H3N2 type, which has been traditionally associated with more severe disease. The good news is that 99 percent of these strains match with what is currently included in the vaccine."
The rest of the flu cases this year are Influenza B, and not as many of those strains are included in the vaccine, but they're also not as serious.
"And among those, 69 percent are matched with the vaccine. These are typically associated with milder disease."
Although there's less protection against Influenza B, it's really Influenza A that's causing most of the problems.
The Centers for Disease Control reports that the strain showing up this year, H3N2, tends to be associated with the worst flu seasons.
CDC officials estimate about two percent of all doctor and hospital visits right now are associated with flu-like symptoms. Those numbers are higher in five states where the flu is especially active, including Texas.
Kathy Barton with the City of Houston Health Department says local cases that have presented this season have been severe, in keeping with the CDC's predictions.
"We started seeing cases back in early December and continue to see cases. I would say we're seeing cases earlier and we're seeing quite a few cases. The good news, though, is that the strains that we're seeing are covered by the vaccine and there's plenty of vaccine still available for people who may not have had their flu shot yet."
Influenza isn't a reportable virus — there's no way to track official rates of infection. But Texas does track pediatric flu deaths and there have already been three this season, including two in the Houston area.
Health officials warn getting the flu vaccine is particularly important this year because of the aggressive nature of this season's virus.