Investigating changes in the immunity systems of people who were critically sick due to coronavirus can be useful in developing new drug and therapies, according to scientists.Experts from Shanghai's Renji Hospital have published an article explaining that the change of B cells' response channel is an important cause for infection and immunity, including serious cases of COVID-19.The discovery was published by world-leading journal Immunity. It can offer new target and research thoughts for the prevention and control of infectious disease, the hospital said.