Only just saw this post - I'm not familiar with the specific story, but the basic principle is that vaccines are less effect if not all people in proximity are immunised. This is because most bacterial and viral infections grow and change at the cellular level, at different rates. This is why you catch a cold every year instead of just once or maybe twice in your life like chickenpox, and why you need regular boosters for things like flu - it's not because it's strong, but because it changes rapidly enough to evade your immune system's developed 'sensors'.
If a virus or bacteria changes too much, then your immune system doesn't recognise it quickly enough, and you get sick.
Humans tend to only catch diseases that come from other humans (stuff like bird flu etc, is the really dangerous stuff, because it can make the jump from animals to people, and your immune system has zero defence) So, what happens in an only partially immunised 'herd' or group of people, disease version 1 can't infect the people who are immunised (their immune system is too good), but it can infect those who are unimmunised.
A side effect, though, of partial population cover is that the infection, if it infects a host and survives for a time, can mutate to some extent (into 'version 2'). The bigger the proportion of people who are not immunised, the more time a strain has to incubate (and the more possible strains there might be). If left unchecked, it gets to the point where all the people who are immunised against version 1 are unprotected, because the virus is up to version 10, and is effectively an unknown organism to your immune system (which is 'trained' to recognise certain diseases by vaccines).
Part of the idea behind vaccination is to protect the herd long term by preventing diseases from finding hosts, so eventually the bacterial/viral organisms die out. Some diseases are gone in the West but prevalent elsewhere, and some things like measles, mumps, whooping cough, are on the rise again in some Western countries when they had virtually disappeared. I'm one of two people who I know have had whooping cough, and that's because we both reacted to the triple antigen as babies and so didn't get the full course of the WC component. But it's a disease on the rise, and probably one of the more lethal of the common vaccine diseases.
If a virus or bacteria changes too much, then your immune system doesn't recognise it quickly enough, and you get sick.
Humans tend to only catch diseases that come from other humans (stuff like bird flu etc, is the really dangerous stuff, because it can make the jump from animals to people, and your immune system has zero defence) So, what happens in an only partially immunised 'herd' or group of people, disease version 1 can't infect the people who are immunised (their immune system is too good), but it can infect those who are unimmunised.
A side effect, though, of partial population cover is that the infection, if it infects a host and survives for a time, can mutate to some extent (into 'version 2'). The bigger the proportion of people who are not immunised, the more time a strain has to incubate (and the more possible strains there might be). If left unchecked, it gets to the point where all the people who are immunised against version 1 are unprotected, because the virus is up to version 10, and is effectively an unknown organism to your immune system (which is 'trained' to recognise certain diseases by vaccines).
Part of the idea behind vaccination is to protect the herd long term by preventing diseases from finding hosts, so eventually the bacterial/viral organisms die out. Some diseases are gone in the West but prevalent elsewhere, and some things like measles, mumps, whooping cough, are on the rise again in some Western countries when they had virtually disappeared. I'm one of two people who I know have had whooping cough, and that's because we both reacted to the triple antigen as babies and so didn't get the full course of the WC component. But it's a disease on the rise, and probably one of the more lethal of the common vaccine diseases.
