Severe cases often involve two phases, explains Mahalia Desruisseaux, MD, an associate professor of internal medicine focusing on infectious diseases at Yale University School of Medicine. As with the flu or other viral infections, Covid-19 typically subsides after several days, because the immune system mounts a response and neutralizes the virus, Desruisseaux says. But for some people, especially those over 65 and those with underlying health conditions and sometimes even in healthy adults and even children, a second phase kicks in.
