Lutz,
It's not so easy to conduct a trial to test efficacy of Measles or Cervical Cancer vaccinations. We do know that in general, not everybody is immune after vaccination and that immunity may be lost over time.
The point of these simulations is to show why widespread immunization matters. Those who are at risk for whatever reason are protected by the immune herd around them if everybody vaccinates. But when people start deliberately not participating, herd immunity fails and even those who vaccinated diligently but are not immune, or those who cannot vaccinate for medical reasons, now are at risk. IOW whether your neighbours vaccinate does matter to you.
"... They ne'er cared for us
yet: suffer us to famish, and their store-houses
crammed with grain; make edicts for usury, to
support usurers; repeal daily any wholesome act
established against the rich, and provide more
piercing statutes daily, to chain up and restrain
the poor. If the wars eat us not up, they will; and
there's all the love they bear us."
-- Shakespeare: Coriolanus, Act 1, scene 1
