The World Health Organization has asked China for details about a rise in respiratory illnesses that has been reported in northern parts of the country, particularly among children. Epidemiologists have warned that as China heads into its first winter since the lifting of zero-Covid restrictions, natural levels of immunity to respiratory viruses may be lower than normal, leading to an increase in infections. Several countries, including the US and the UK, experienced large waves of respiratory viral infections in the first winter after Covid restrictions were lifted as people had…