Today’s post looks at how serious measles is and what difference vaccination against measles has made.
How serious is measles?
Very. The Lay Science blog has covered this topic here. The post includes details of recent outbreaks of measles:
Italy, 2002: 4 deaths, 594 hospitalizations.
California, 1989/90: 75 deaths, 3,390 hospital admissions.
Japan, 2000: 88 deaths.
Germany, 2006: 160 children hospitalized, 3 with brain inflammation.
Ireland, 2000: 3 children dead, 350 hospitalized.
This “MMR the Facts” PDF has a list of the complications of measles and how frequently they are likely to occur:
ear infection (1 in 20)
pneumonia/bronchitis (1 in 25)
convulsion (1 in 200)
diarrhoea (1 in 6)
hospital admission (1 in 100)
meningitis/encephalitis (1 in 1,000)
late onset: SSPE* (1 in 8,000 children
under 2 years old)
death (1 in 2,500-5,000)
*Subacute sclerosing panencephalitis (SSPE) is a rare, degenerative neurological condition that can develop some years after natural measles infection and causes brain damage and death. The risk is greatest in those who were infected at a young age. The average interval from measles infection to onset of SSPE is around 8 years. Death invariably follows. Since the introduction of live attenuated measles vaccine in the 1960s, the incidence of SSPE has dramatically decreased and we expect the death rate from SSPE to fall even further. Measles vaccine directly protects against SSPE.
Convulsions, inflammation of the brain, and death seem to me to be pretty serious complications. In fact, in America, of the 501 measles cases reported during 2000-2007, one in four patients was hospitalized, and one in 250 died. This is referred to in the Lay Science blog post and the original source is this page.
How effective is vaccination against measles?
If you prefer numbers to graphs: HPA has some.
The 10 years prior to the introduction of the single measles vaccine (1958-1967) brought 863 deaths (and 4,120,936 notifications) and in the 10 years following the introduction (1968-1977) there were 292 deaths (a fall of 571 deaths – or 66%) – and 1,600,979 notifications (a fall of 2,519,957, or 61%).
The last 10 years of the single measles vaccine saw 837,424 notifications of measles and the first 10 years following the introduction of MMR saw 106,210 notifications of the disease. This is a fall of 731,214 (87%). Deaths in the 10 year period 1979-88 were 140, 10 year period 1989-98 were 18 – a fall of 87%.
So, deaths and notifications both fell about 60-65% following the introduction of the single measles jab in 1968 and deaths and notifications both fell a further 87% following the introduction of the MMR triple vaccine in 1988.
What happens if we reverse this trend? All we need to do is stop vaccinating our children and this is what we see – by 2003 MMR coverage was down to 82% (BBC report), which is represented by this graph:
Following the drop in MMR uptake, there was (unsurprisingly) an increase in cases of measles:
Hundreds died because of measles in the ten years prior to the introduction of MMR. Less than twenty died for this reason in the ten years following the introduction of this vaccine. As vaccination levels drop, measles notifications increase and the number of deaths inevitably increases. How many lives have these vaccines saved? How many people have been spared serious complications? How many people have avoided being infected with measles?
I’ll try to give an answer to the final of those three questions first: in the period from 1940 to 1968 (the year the single measles vaccine was introduced), there were 11,337,267 notifications of measles infection – a rate of 390,940 per year over the 29-year period. In the period following the introduction of the single measles vaccine and leading up to the introduction of the MMR vaccine, there were 2,326,316 notifications, a rate of 116,316 per year over the twenty year period. So it looks like the single measles vaccine may have prevented around five and a half million cases of measles in the period in which it was used (this is only hypothetical, but a reduction in the average number of cases per year of 277,624 over twenty years gives you 5,492,489). Five and a half million cases equates to 275,000 incidences of convulsions or 550,000 cases requiring hospitalisation according to the figures provided by MMR The Facts (1 in 200 and 1 in 100 respectively). The introduction of the MMR vaccine has seen an average of 109,429 fewer cases per year – over 19 years, that comes to about 2 million cases of measles (2,079,154 if my sums are correct). Again using the figures from MMR The Facts, this number of cases would equate to 100,000 incidences of convulsions and 200,000 cases requiring hospitalisation over the period of use so far. That’s an awful lot of people who avoided becoming seriously ill through measles infection and it looks like it is thanks to vaccination.
Deaths: there were 7,863 deaths in the period 1940-1968, with 5,687 occurring in the ’40s, 1,409 in the ’50s, and 767 from 1960-1968 (about 85 per year). Following the introduction of the single measles vaccine, deaths fell to about 20 per year (401 over twenty years of use). The introduction of MMR saw deaths fall still further to about 1.5 per year (27 over 9 years of use). From 85 deaths per year in the last nine years without vaccination down to 20 deaths per year in the twenty years we used single measles vaccine and then further down to 1.5 deaths per year – that means that (hypothetically) 1300 fewer people died during the period in which we used the single measles vaccine than otherwise would have done. A further reduction of 18.5 deaths per year over the nineteen years we have used the MMR vaccine equates to an extra 350 lives saved.
Some graphs were pinched from here, here and here. The media’s coverage of MMR, Andrew Wakefield’s approach to science, and the anti-vaccination movement have all been criticised on some of the blogs aggregated at badscienceblogs.net – e.g., this list of blogs covering MMR. The Bad Science blog itself has an archive containing 39 posts on MMR.