While flu cases are still low nationally, more than 90 percent are among children and young adults ages 5-24, according to the CDC.

Most cases are of the H3N2 lineage – a strain health experts say is particularly troublesome as it tends to mutate faster than other variants of influenza. The last time H3N2 was the dominant strain was the 2017-18 flu season, when the United States saw 710,000 flu-related hospitalizations and 52,000 flu-related deaths, the worst since the 2009 H1N1 flu pandemic…

The flu season typically runs from October to as late as May, with activity tending to peak between December and February, according to the CDC.