The coming flu season is on track to be much worse than the last cycle, according to health experts, who fear an influx of cases could further strain hospitals already overwhelmed by the Delta surge.

The season could also strike earlier and more severely than usual, doctors and researchers said, because many people haven’t been able to build up their natural immune defenses while working from home and avoiding strangers.

“The worst case scenario is a real twindemic” of Covid-19 and flu cases, said William Schaffner, professor of preventive medicine at Vanderbilt University School of Medicine.

Several factors are behind the expectations for a potentially difficult flu season, Dr. Schaffner and other health experts said, though it is notoriously hard to predict how badly the virus will hit.