Vaccines are a plot by big pharma!

[Michael]

This is a subject that causes strong emotions in people, and it can be difficult to just focus on what we really know. (By chance I did a little work with Andy Wakefield around the time he was looking at the link between measles, measles virus and Crohn's disease.)

So what do we really know? Well, the people who do the most thorough and respected reviews of all the available evidence are the good people at Cochrane, who have developed thorough methods for reviewing a wide range of evidence on any particular question.

You will find their summary on MMR here: Cochrane review on MMR

It may be a little frustrating for people because what it says in the abstract is "Exposure to the MMR vaccine was unlikely to be associated with autism, asthma, leukaemia, hay fever, type 1 diabetes, gait disturbance, Crohn's disease, demyelinating diseases, bacterial or viral infections", but also that "The methodological quality of many of the included studies made it difficult to generalise their results."

So the risk of a link to autism or Crohn's disease (Andy Wakefield's original concerns) appears to be low, but that we don't have the necessary quality of study to be absolutely sure how low it is.

A couple of related things I would say are:

1) Andy's work initially identified a link of the measles virus itself to Crohn's disease. He then suggested it could also be caused by the vaccine (now considered unlikely). Even if Andy was right (which very few people now think), we wouldn't help people by withdrawal of vaccine if they then got measles itself, because Andy's hypothesis was that both could lead to Crohn's disease (by the time he moved onto autism he wasn't really looking for links to the virus itself, by then he'd got the bit between his teeth on looking for potential links with the vaccine).

2) Any vaccination carries some very small risk. The Cochrane review highlight's known risks. And here is where the issue is. So long as 90% or more people are being vaccinated than the disease spread is blocked by 'herd immunity'. Those that don't have the vaccine are effectively protected by those that do. So a small number of people can avoid the very small risks of vaccination without being at significant risk of the infectious disease itself. It's not 'fair', but it's real. But as vaccination drops below about 90% then the disease can start spreading again and suddenly people are now at a much more significant risk of contracting the disease. Now the balance of risk is such that vaccination is much the better option. Where we seem to be on the MMR virus is generally just the right side of the required vaccination level; those who are particularly worried about the vaccine can get away with not using it because they are protected by the majority of others that are vaccinated. But we are seeing some occasional local outbreaks of the viruses. That is usually enough to cause a reflex increase in vaccination rates. It is, to some extent, a self-correcting system - fewer people object to vaccination when the disease is present in the community, though of course it can be too late for some by that point who may suffer long term effects of infection (or, in the case of Rubella it is of course the unborn child who suffers the consequences of the lack of vaccination).