You can't get herd immunity from a vaccine that does not stop the spread of the disease, even with 100% coverage. Covid starts spreading early in the infection,

You can't get herd immunity from a vaccine that does not stop the spread of the disease, even with 100% coverage. Covid starts spreading early in the infection, before your vaccine-stimulated antibodies get into the action. For that kind of contagion, vaccines cannot stop the spread. For other diseases that become contagious later in the infection, vaccines can, and at the outset it seemed like Covid might behave that way, but it turned out not to. What the current vaccines can do, is lessen the possibility of serious outcomes, which is great.