|Zhong Kui, a Chinese god, punishing two gods of measles (1862)
I’ve talked before about measles incidence and the effect of vaccination. Now I’m going to spend this whole week talking about measles deaths, because I ended up with more than I could cover in one or two posts. So this is Part I of a five-parter.
A group of diseases which … even now are considered to be unavoidable are scarlet fever, measles, and whooping cough. … According to the statistics collected in the census of 1900, these three diseases were responsible for upward of thirty thousand deaths in the course of a year.”
–”The Conservation of the Child”, by Earl Mayo. in The Outlook. A Weekly Newspaper. Volume XCVII. January-April, 1911 (pp. 893-903)
That was the situation in 1911 and in the early 20th century generally, and for centuries before that. Almost every child caught measles, and a lot of them died. Measles wasn’t quite as lethal as smallpox, but it wasn’t too far behind:
Measles should no longer be considered a “minor” infection. It is a major illness causing a considerable mortality and a much greater morbidity among young children affected by it. 1
(By the way, as well as citing my direct quotes in footnotes as usual, I’ve collected the 40-odd references I read while trying to figure this story out and put them up here.)
But, starting somewhere around 1915, that began to change. Very gradually (so gradually that it almost escaped attention) measles stopped being a fatal disease. In 1945, William Butler said:
In three-score years or so, during which the population of England and Wales has nearly doubled, the gross annual contribution of deaths from measles has fallen to about one-twelfth of the mean figure at which during several quinquennia it stood in the eighties and nineties of the last century. Nor is there reason to believe–on the contrary–that measles is now less prevalent than it was. It is still true that nearly everyone at one time or another has measles. 2
And the trend didn’t stop there. In 1945, about 163 out of every 100,000 measles cases died. In 1955, just 25 of 100,000 died, and it’s hovered around there since.
In other words, a person who caught measles in 1900 was between 40 and 150 times more likely to die than someone who caught the virus in 1955. You can play with the numbers in various ways, but no matter what you do there has been an absolutely, spectacularly, incredible drop in measles case-fatality rates.
Below are a couple of charts to illustrate this. The UK (number of measles deaths in England and Wales) is on the left, the US (measles deaths per 100,000 population) on the right (click for larger versions). The dashed blue lines are the actual numbers. Because measles is a very, very epidemic disease, the numbers change hugely every year, so I’ve applied a crude smoothing to the raw numbers (the green solid lines) to make the trends easier to see. My US numbers only go up to 1940, but here’s a chart through the 1960s, if you like – there’s no surprises in it, it’s pretty much like the UK.
|Measles deaths in the UK, 1900 – 1965||Measles deaths in the US, 1900 – 1940|
Important note: In England, measles was not a notifiable disease between 1919 and 1939 (and I believe the rules for notification changed for a few years before 19193 as well), and the effect of this is easily seen — the abrupt drop in reported deaths just before 1920, and the flatter line for a few years afterward, is almost certainly not real (I’ve boxed that non-notifiable period off in red.) But the overall trend is still easy to see even so.
This had nothing to do with the measles vaccine, because this survival increase happened entirely before the vaccine was available in 1963. There was essentially no change in the number of measles cases over this period (adjusted for population, of course), it’s just that once you caught measles you weren’t as likely to die. And case-fatality rates didn’t change significantly after the vaccine was introduced. The death rate per case in 1955 (pre-vaccine) is pretty much what we see today in first-world measles outbreaks.
The vaccine did spectacularly reduce the number of cases, of course, and therefore did reduce the total number of deaths. Also, equally obviously, vaccines aren’t only given to prevent deaths. Even if measles doesn’t actually kill your child, she’ll still, quite possibly, be pretty sick; there’s a pretty good chance she’ll be hospitalized; and a significant number of survivors have some form of medium- or long-term complications.
Was measles unusual? Overall mortality, and especially childhood mortality due to disease, did drop over this period, and quite dramatically so:
The infant mortality rate has shown an exponential decline during the 20th century. … For children older than 1 year of age, the overall decline in mortality during the 20th century has been spectacular. … Between 1900 and 1998, the percentage of child deaths attributable to infectious diseases declined from 61.6% to 2%. 4
Here’s the famous chart of 20th-century mortality.5 (Note the brief, huge spike in 1918, due to the 1918 pandemic influenza!)
|Mortality rates in the US through the 20th century
So yeah, in general mortality rates did improve greatly since 1900, flattening out in the 1950s, just the same pattern as with measles deaths. But check the scale, and compare to the UK (especially) chart above: Measles outpaced this overall improvement, and by a huge amount. Overall, during this period childhood mortality rates improved perhaps 8-10-fold — clearly a tremendous improvement, but still, at best a quarter of the improvement in measles survival. (And measles was a late starter, too — overall mortality had been dropping for at least 15 years before measles case-fatalities started to go down.)
So what happened between 1915 or so, when measles death rates began their decades-long drop, and 1955, when the drop stopped? That’s the subject of this entire week’s worth of posts, but to give you a peek at the answer I came up with: It beats the hell out of me. There really isn’t a single, simple explanation for this, as far as I can find.
(I’m not a historian, a medical doctor, or a measles researcher, and I’m more than happy to be corrected. Anyone who has actual information on this, please let me know. If you have an opinion, no offense, but I’m not interested unless you have data to back it up.)
The problem is that the usual answers are either too vague to be useful (what exactly does “quality of living” mean, medically?) or inadequate (improved nutrition is certainly important, but as far as I can see probably only improves survival maybe 5-fold, not 100-fold). Specific advances (antibiotics, etc) undoubtedly helped, but you don’t see abrupt short-term drops in mortality, as you’d expect if any single advance was a major factor; rather, you see a constant, gradual, improvement.
I’m left with the unsatisfying conclusion that either a conglomeration of many factors may have acted together (the most likely situation, and that’s what the real world is often like — no simple answers), or that there’s some specific factor that I haven’t found out about. I’ll talk about specific causes later this week.
Here’s my plan for Measles Week:
- Monday: Explanation of the question, and evidence for it being a real question. Done!
- Tuesday: History of measles virus
- Origins and impact
- Wednesday: Answers that are (probably) wrong
- Changes in surveillance or notification
- Change in the virus
- Antiserum treatment
- Thursday: Answers that (might be) right
- Vitamin A
- Less overcrowding
- Antibiotics and other treatments
- Demographic changes
- Friday: What would measles be like today, without the vaccine?
- Mortality and complication rates in modern 1st-world epidemics
Put on your party hats, blow up a balloon, pull up a chair, and stick around.
- Prevention of Measles in a Children’s Hospital. W. E. Crosbie. Br Med J 1938;1:1003-1004[↩]
- The Fatality Rate of Measles: A Study of its Trend in Time William Butler Journal of the Royal Statistical Society, Vol. 108, No. 3/4 (1945), pp. 259-285[↩]
- Butler W (1945) The Fatality Rate of Measles: A Study of its Trend in Time. Journal of the Royal Statistical Society 108:259–285.[↩]
- Guyer B, Freedman MA, Strobino DM, Sondik EJ (2000) Annual summary of vital statistics: trends in the health of Americans during the 20th century. Pediatrics 106:1307–1317.[↩]
- Armstrong, G. (1999). Trends in Infectious Disease Mortality in the United States During the 20th Century JAMA: The Journal of the American Medical Association, 281 (1), 61-66 DOI: 10.1001/jama.281.1.61[↩]