> One of the things that makes SARS-CoV-2 such a problem is that people get contagious long before they show symptoms. I also wonder how effective the vaccine

> One of the things that makes SARS-CoV-2 such a problem is that people get contagious long before they show symptoms. I also wonder how effective the vaccine is at preventing its receivers from even reaching that asymptomatic but already contagious stage. If "90%" is just "90% less reach symptomatic stage" then the percentage of receivers that are prevented from reaching contagiousness could be much lower. This would basically mean that the virus is almost guaranteed to become endemic despite vaccination (unless another vaccine also removes the contagious stage quite well) and that everyone who doesn't get a vaccine will eventually test their immune system against the virus. Natural immunity often follows a similar pattern. After a while you become susceptible to a light reinfection but the immune system will be in a very good position for a quick - but not instantaneous - victory on its second encounter with the virus. Under those circumstances, herd immunity effects fail to realize unless the first wave is so lightning fast that it fizzles out before the immune systems of early survivors (or the similarly vaccinated) fall back into standby mode.