A delayed surge of the respiratory syncytial virus, usually seen in young children during the winter, has hit southern states especially hard this summer with a simultaneous rise in COVID-19 infections due to the delta variant, adding to concerns that hospitals will be strained.

The rise in new RSV cases coincided with the retreat of the pandemic earlier this year, and physicians say they suspect that social distancing, face masks, and other efforts to check COVID-19 suppressed outbreaks last season.