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This flu season is on track to be one of the worst in 15 years, with nearly 12,000 people needing to be hospitalized, federal health officials reported Friday.

The latest weekly report from the Centers for Disease Control and Prevention shows that the season, which started early and hit many states simultaneously, continues to blanket the country.

The virus has killed at least 37 children so far, with seven deaths reported in the week ending last Saturday. By the end of this season, officials said the pediatric death toll is likely to approach, if not exceed, the 148 deaths reported during the 2014-2015 flu season. The influenza currently circulating is the same virulent strain that predominated three years ago.

As of Saturday, flu activity was reported as high, if not extreme, in 39 states plus Puerto Rico and New York City.

“It’s a tough flu season,” said Daniel Jernigan, who heads the CDC’s influenza division.

More people are seeking care for flu-like illness than at any time since the 2009 swine flu pandemic that swept the country. If that pandemic season is not included for comparison, the last time the country experienced such high levels of influenza-like illness was in 2003-2004.

The vast majority of current flu illness is from a particularly nasty strain of virus known as H3N2, which is associated with severe illness in young children and people 65 and older. But compared with previous seasons when this strain also dominated, officials are seeing two notable differences.

First, flu hit almost all the states at the same time, Jernigan said. Second, “flu activity has stayed at the same national level for three weeks in a row. We often see different parts of the country light up at different times, but there is lots of flu all at the same time.”

The percentage of people visiting clinics and hospital emergency rooms and doctor’s offices is at the highest level of the season and only outstripped by numbers during the pandemic of 2009-2010 and the seasonal flu season of 2003-2004, Jernigan said.

The rapid increase in cases came right after the winter holidays, he noted, and likely was triggered by children returning to school and spreading the virus.