It matters when you break it down and ask, "Effective against what?" Death? Hospitalization? Disease? Infection? The numbers you mentioned refer to effectiveness (inasmuch as that is different from effectivity) against disease. The effectivity of J&J is about 75%. Modern 93%, and Pfizer 95% IIRC. A complication is that among the different vaccine manufacturers there are slightly different definitions of "disease." During their stage three trials the vaccines were tested against disease, however defined, and not against infection, which is more difficult to test for. The initial and understandable concern was to get people to stop getting sick and dying. To determine if the test subject is sick you just have to ask, "do you have any of these symptoms." Not so with infection. You have to test for that. So to get the vaccines out ASAP & start saving people from dying they used the simpler way of going about it.