MIAMI, United States (AFP) — Flu is sweeping the United States, killing at least 37 children as influenza sends the most people nationwide in search of medical care since the 2009 “swine flu” pandemic, US officials said Friday.

This year, the most common strain is H3N2, and nearly every state has been hit hard, said the US Centers for Disease Control and Prevention.

“For the past three weeks the entire country has been experiencing lots of flu, all at the same time,” said Dan Jernigan, director of the Influenza Division at the National Center for Immunization and Respiratory Diseases, part of the CDC.

This marks the “most flu activity since 2009,” he told reporters on a conference call.

A total of 6.6 percent of all people going to clinics and emergency departments this season did so because of the flu, he said.

“This is the highest level of activity recorded since the 2009 pandemic which peaked at 7.7 percent.”

The 2009 H1N1 pandemic, then known widely as “swine flu,” swept 206 countries and overseas territories and killed more than 6,770 deaths, according to the World Health Organization.

If the 2009 pandemic is not included for comparison, because it was considered such an outlier, the most recent season when as many people sought care for the flu in the United States was 2003-2004, when the level peaked at 7.6, Jernigan said.

What really sets this season apart is that “flu activity became widespread within almost all states and jurisdictions at the same time,” said Jernigan.

“Flu activity has stayed at the same level — at the national level — for three weeks in a row, with 49 states reporting widespread activity.”

The bulk of flu cases have been among senior citizens — those 65 and older — and baby boomers aged 50-64.

The true severity of this season will not be known for months, until all the data is collected and analyzed.

The season is only about halfway through.

“In past seasons that are like this one, we have estimated that by the end of the season, 34 million Americans had gotten the flu,” Jernigan said.

During H3N2 outbreaks in past seasons, about 56,000 people on average have died, he added.

“We anticipate there will be more pediatric deaths this year,” he added, saying the actual number of children who have died from the flu so far this season may be twice the current estimate.

A big concern is the high number of cases of H3N2 — the most common strain this season — which tends to be more deadly than other types of the flu.

Health officials are still urging people to get vaccinated despite questions about the shot’s effectiveness.

“The vaccines just don’t do that well against H3N2,” said Jernigan.

“The immunity that was gathered last year may not be enough to prevent another wave of H3N2 this year.”