When flu infects a cell, the cell starts to make the virus subcomponents, and it then starts to build complete infectious virions. Usually the cell ruptures and

When flu infects a cell, the cell starts to make the virus subcomponents, and it then starts to build complete infectious virions. Usually the cell ruptures and all the complete virions start to look for their attachment part on the cell. With Covid 19 = the spike. With flu it is sialic acid = endocytosis = merges with and through the cell membrane. There are a number of subcomponents in a virus. When the cell bursts open, the cell can not longer continue making virions = all the parts of the cell spill out and the body deals with them as foreign = immune system absorbs them and also the adaptive immune system makes antibodies and memory cells learn all of them as separate antigenic particles for which it makes antigens. These parallel antigens give a broad and deep immune response - this happens with COVID or FLU = why the immunity of a true infection is stronger and longer lasting than a spike response. Measles is large, when the cell breaks it spills out a huge pack of fragments of many types = very long lasting immunity. Measles vaccine 14-20 year, which, so when the orthodox jewish groups had deaths among children who attended measles parties, they also had illness among older Jewish people who were vaccinated a long time ago. Later Jewish people do not take vaccines for religious reasons. An older cadre of Jewish people who had infections in youth did not get infected as their immunity was almost life long.