Vaccination

Despite the clear success of vaccination in the control of a number of infectious diseases, there are still far too many people who decline vaccination, for themselves or for their children. Why is this, and why does it matter?

The reasons fo declining vaccination, ignoring inertia, are i) doubts over the effectiveness of vaccines and ii) concerns about safety. The first point is totally unfounded. Smallpox was completely eliminated, in large part due to the success of the vaccine. Polio has been almost eliminated – and could be by now if the few countries where it still exists were not so resistant to use of the vaccine. Diphtheria, tetanus, – the list goes on.  All the vaccines in current use have been shown to be effective (leaving aside the use of BCG for control of TB, which is a complicated question).

That brings us to the safety issue, and especially the MMR (measles, mumps, rubella) vaccine. In 1998, Andrew Wakefield and colleagues published a paper describing a study of 12 children with autism and chronic intestinal disorders. An incidental finding was that most of these children had received MMR. Although the paper actually states that they did not prove an association between autism and MMR, it was widely believed that they had. This erroneous belief still persists, despite numerous large and well-conducted studies that have failed to find any association whatever, and despite the fact that the Wakefield paper has now been withdrawn. To a large extent, the misplaced belief is fuelled by the fact that the age at which the MMR vaccine is given is the age at which signs of autism often first appear – so it is inevitable that in some cases autism will show up soon after the vaccine is administrered.

A very similar situation arose in the 1970s with the whooping cough (pertusssi) vaccine, where some children showed neurological problems after having the vaccine. This wasn’t anything to do with the vaccine – it’s just that some children do have these symptoms at about that age. But the unjustified fear of the vaccine led to a decline in its uptake, with the consequence that in the winter of 1978-79 there wee 100,000 cases in the UK, with many deaths and even more neurological problems.

Finally, does it matter if some people refuse the vaccine? Isn’t it a matter of personal choice, to accept the risk of getting the disease? The answer lies in the question of how can we protect those who cannot be vaccinated – especially very young children who are too young to be immunised (because their immune system is not fully devloped)?

Spread of a disease depends on an infected person coming into contact with others who are susceptible to the disease. If you can reduce the proportion who are susceptible to a low enough level, then the disease will not spread. This is known as herd immunity. For smallpox, it was quite easy – only about 75% needed to be vaccinated to stamp out the disease completely. Measles is much more infectious, and the critical level is much higher – about 95%. Failure to achieve that level means epidemics will occur – and they are occurring. So those people who refuse vaccination are not only putting their own children at risk, but they are putting others at risk, including all those babies who cannot be immunised.

For a more complete coverage, read my book Understanding Microbes