While pandemic measures appeared to keep the flu at bay, this year experts are again concerned, especially as some countries and state authorities roll back lockdown rules. Many officials and experts are urging the public: Do not dismiss the danger of the flu, and seek a flu vaccine.

“This year we are guaranteed to have the flu, and we are going to have some version of a twindemic,” said Dr. William Schaffner, the medical director for the National Foundation for Infectious Diseases. “It could really further strain an already extraordinarily stretched, strained, tired-to-the-bone health care system.”…

The relative lack of flu cases over the last 18 months could also mean that population-level immunity to the flu is lower this season, said Lynnette Brammer, the leader of the C.D.C.’s domestic influenza surveillance team.

And while it is still uncertain how the season will play out, she added, relaxed pandemic measures in some places will “likely result in the resumption of seasonal flu virus circulation.”