pixie: "I haven't seen those. But, isn't it the case you have to catch it first, for your body to kill it off? It won't just deflect off you, because of a vaccination?" - yes of course, that's the point. If the virus enters a vaccinated person it'd be like a Spurs fan going into an Arsenal pub on match day. It will be fought off by the immune system, yes a brief infection will be present but the virus will not be able to multiply and do the damage it does. The viruses will get swept up by the immune system or just die naturally.