Would a person's lifestyle affect the rate at which the body fights Covid-19? Like, would two people with one being in better shape (assuming that both have no outlying health conditions) see differences in their infections?
being more healthy is certainly one factor, but it is more likely your genetics. Your immune system is unique to you because of proteins called the HLAs and no two peoples collections of HLAs are the same. HLAs are the basis for tissue typing and the reason that organs for transplanting have to be as close as possible. Particular HLAs are linked to particular immune responses even to viruses. Researchers are beginning to type people looking for linkages between HLAs and response to SARS-CoV-2.