How We Conquered Measles

In 1915, in England & Wales, there were 16,455 deaths from the measles; 70% of measles deaths were children aged 1-4. Measles was the biggest killer of toddlers, responsible for 20% of all toddler deaths.  It was also the 2nd biggest killer (behind diphtheria) of children aged 5-9. Although 1915 was a peak year, the average at the time was around 10k total measles deaths per year. 

In 1994, there were no measles deaths at all. From then until now, there have been few years where we have had more than one measles death.

How did we achieve this? How did we conquer measles? 

The answer can be found in this chart that shows the number of measles deaths (black) between 1901 and 2016, and the number of measles notifications (red) between 1940 and 2016.

1915 to 1955: Dramatic Reduction in CFR

From 1915 to 1955, measles deaths reduced by 99%, from over 10,000 deaths per year to below 100 deaths per year.

Most of the decline happened between 1915 and 1935.  In 1935, there were only 1,346 deaths from measles, a reduction of 92% over a 20-year period.  The measles death rate fell even faster than the overall infant mortality rate; it was now responsible for only 7% of deaths of children aged 1-4 (now only the 3rd biggest killer), and only 2% of deaths of children aged 5-9 (now only the 10th biggest killer).  

In 1955, there were only 176 deaths from measles, a reduction of 99% over a 40-year period.  In most years of the 1960s, there were fewer than 100 measles deaths per year, and measles was no longer among the top 10 killers of children of any age group. Measles was now responsible for only 3% of deaths of children aged 1-4 (the 7th biggest killer) and 2% of deaths of children aged 5-9 (the 9th biggest killer). 

Turning now to measles notifications, for which we have data only back to 1940, we can see that the number of notifications of measles was flat from 1940 to 1968 (the pre-vaccine period), at around 400k on average. The driver behind the dramatic decrease in the number of deaths was therefore a dramatic reduction to the Case Fatality Rate (CFR), i.e. the number of deaths per case (or the inverse of the survival rate). Just as many children caught measles, but far fewer died from it.

We can use notifications as a proxy for cases to calculate the CFR for the period after 1940. To estimate the CFR for the period 1901-1940 we need to use birth numbers, as in the following chart:

By assuming a similar proportion of children caught the measles before 1940 as in 1940-68 (i.e. most of them), we can extrapolate the CFR backwards, giving us the following chart:

The CFR prior to 1915 was over 2%, meaning that 1-in-50 children who caught measles died from it. By 1940, it had decreased to 0.2% (1-in-500), and by 1955 it had decreased to just 0.02% (1-in-5000). This is a 99% reduction in the CFR. This reduction in the CFR is why measles was no longer considered a serious, life-threatening illness during the period 1955 to 1968; 99.98% of children survived it. The average number of measles deaths per year was down to below 100 by 1955.

1955 to 1968: CFR Stops Decreasing

In 1955 the incredible reduction in the CFR suddenly stopped. It remains at around 0.02% even today, as can be seen in this chart:

Let us now re-scale the deaths axis of our first chart to see what this meant for the deaths figures after 1955:

As a result of the flat CFR, the number of deaths stayed at just below 100 per year for the period 1955-1968. The record lowest numbers of measles deaths in the pre-vaccine era were in 1956 (30 deaths), 1960 (31 deaths), 1962 (39 deaths). The most deaths in this period were in 1961 (152 deaths), 1963 (127 deaths), and 1965 (115 deaths) and no other years in this period had more than 100 deaths.

1968 to 1997: Vaccines Reduce Measles Cases

From 1968 to 1997 there was a 99% reduction in measles cases. The majority of that reduction followed the introductions of the measles vaccine (1968) and the MMR vaccine (1988). From 1968 to 1971, the annual number of measles notifications fell by over 60%, from 400k to 150k. From 1988 to 1991, notifications fell by 90%, from 100k to 10k. With a flat CFR, the 99% reduction in cases from 1968 to 1997 meant a 99% reduction in deaths, from 100 per year before vaccines down to just 1 per year.

1997 to present: Measles Now Rare

In most years since 1997, there have been under 5k cases and rarely more than 1 death, as we can see by one final re-scaling of the chart:

How then did we conquer measles?

Measles killed over 10,000 per year before 1915 but fewer than 100 per year by 1955.  This 99% reduction in measles deaths was due to a dramatic reduction in the deadliness of the disease between 1915 and 1955.  This could have been due to a healthier environment (higher standards of hygiene, better sanitation systems, more nutritious food, cleaner drinking water and air, less cramped living and working conditions, etc) or to better treatment of measles cases (improved medical knowledge among doctors and the public, better access to healthcare, more effective quarantine procedures, etc), or both. 

The healthier environment and better quality treatments deserve credit for making measles a relatively mild disease; these developments saved thousands of lives each year, just in England & Wales. The measles and MMR vaccines reduced the number of measles cases and measles deaths by another 99%, saving dozens more lives per year. Vaccines deserve credit for making it rare for anyone to suffer from the measles.