Numerous studies show that Covid is most transmissible in the first week to 10 days of an acute infection. Attempts to culture virus collected from infected people show that it is not capable of replicating itself after day 9, even if the patients still have high levels of the virus. The symptoms of long Covid are believed to reflect not the direct action of the virus itself but the body’s response to that virus. It is probably safe to assume that those with long Covid cannot pass the virus to others; it is also the case that the last word has not yet been written on how long people remain infectious.