Friday 11 December 2015

The Measles

In 1977, when The Boy was 18 months old we set off in a Citroen Dyane from Dublin for Siracusa in Sicily. On the return journey we exchanged petrol vouchers for soup. There was no spare money, so we drove to Larne in The North to catch a ferry to Scotland en route for Dover. Clearly a 300km detour North was not the most efficient use of our time, but we were strapped for cash and that was the cheapest costing.  On the ferry to Stranraer the poor wee mite went all spotty before our very eyes: it was the rubeola!
Here's a brilliant data-rich graphic that won an award at the information-is-beautiful awards this year. I've clipped the more recent data columns to make it fit on my page:
If you think that measles is something that you should be frightened of, then this shows that vaccination works: within a few years of being introduced, the incidence of measles fell off a cliff from 1-4% of children infected every year to being an endangered species.  If you check out the original sources, you can see that for the last 6 or 7 years, across the whole country there has been a bit of a pickup in measles. I'm not sure if this is an artifact of the data. In a well-fed nation like the US, the rate of death among those who contract the virus is 1 or 2 per 1000 cases.  Manageable, says you, but still bad enough for those two parents in every small town who have to bury a small white coffin.  And a little more serious when, back in the 1950s 90% of US children were infected with measles with a jumbo-jet full dying each year.  In less well fed places, the mortality rate goes up 50x to 10%.  Other sub-lethal problems include scarring of the cornea, pneumonia, encephalitis and ear damage.  And don't take your measles-infected child to visit Uncle Jack with AIDS - it could be a fatal encounter for Jack.

Because measles is so infectious it romps through communities in epidemics and then romps back again when a new cohort of susceptible infants is born.  If you can reduce the infectible population size sufficiently, the measles romps through and then dies out for lack of places to propagate. It's much more serious if you catch the disease as an adult and this is a problem for island populations that have eliminated the virus when measles is reintroduced after many years absent. This is the reduce-the-effective-population-size argument for immunization. The rate of vaccination to achieve 'herd immunity' in measles is about 95% - this key epidemiological figure is different for different viruses which may be less, or more, infectious. Measles appeared in human populations in medieval times, probably as a mutating rinderpest virus from cattle. Like ebola in the old days of static isolated populations, that first rinderpest-like invasion would have died out in earlier times. But the beginnings of urbanisation and increased travel brought the effective population size up above 1/2 million people.  This was enough victims to sustain measles in cyclical sweeps through the human youth.

Any community can carry a few people who choose not to vaccinate because of religious scruples or a belief that vaccination is in itself harmful - causing autism, hammer-toes and hallucinations. There is no real political will to try to eradicate measles virus as we have done with smallpox partly because the fatality and morbidity rate is comparatively low. I mentioned Ali Maow Maalin a year ago as the last person to contract smallpox in the wild in 1977.  WHO declared the virus extinct on 9th December 1979.  I'll have to write something about polio one of these days, which really put the fat in the fire in America in the 1950s.

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