Covid: The warning sign of the newest Omicron strain that's striking sufferers at 'night'

THE LATEST surge in coronavirus cases, driven by the highly transmissible Omicron subvariants BA.4 and BA.5, is a reminder that the fight against Covid is far from over. Some scientists have been finding subtle differences in the illness caused by the newest strains compared to their predecessors. One warning sign, an immunologist has warned, is emerging at night.