We may have a vaccine for Covid-19 by late this fall. By winter, we could have several. And if all goes as planned, each vaccine will be accompanied by data demonstrating that it reduces the risk of developing Covid-19, the clinical syndrome caused by infection with the novel coronavirus.
But we won’t know which of these vaccines is more effective at preventing Covid-19, or have much idea if one or more of them reduce the risk of a person becoming an asymptomatic carrier of the virus. We also won’t know if the duration of immunity is similar between the vaccines, or if the side effects are equally tolerable.