PHILADELPHIA — The flu is poised for a comeback this year after two seasons in the shadows of the COVID-19 pandemic. Influenza circulates year-round in the United States but the virus is most active in the winter. Cases usually start climbing in October or November, peaking around January or February, and declining through May. In a regular season, the flu leads to as many as 710,000 hospitalizations and 52,000 deaths including up to 200 children, according to the Centers for Disease Control and Prevention. Then came COVID-19. People stayed home, wore masks, and kept a safe distance from one …