> 90% still crushes the transmission rate. Unfortunately, there's yet another property of vaccine performance: some prevent the virus from reaching any level o

> 90% still crushes the transmission rate. Unfortunately, there's yet another property of vaccine performance: some prevent the virus from reaching any level of footing in the host, others only make the body's eventual response stronger, preventing initial footing to cause heavy illness. SARS2-COV is rather peculiar in how its transmission performance is particularly strong in early, mostly presymptomatic stages, so it's perfectly possible to end up with a vaccine that reliably protects carriers from disease, but does not remove them from the spread equations at all, or only very little.