Measles: the canary in the coal mine

Today we learned that the annual number of global measles deaths increased from 2014 to 2015, up from 115,000 to 134,000. This is a disturbing turn of events that we urgently need to address. Not just because the vast majority of these deaths are vulnerable children under the age of five, but also because measles outbreaks are usually indicative of an even deeper problem.

Measles is one of the most infectious diseases known to humanity, so contagious in fact that it is possible to catch it just by entering a room hours after an infected person has been there. Because of this immunisation coverage has to be much higher across a population for measles than for most other diseases, typically with more than 95% of the population covered, in order to achieve herd immunity.

It is precisely because of this that measles prevention is considered such an integral part of the global-health agenda: the contagious nature of the disease makes it a good proxy for assessing immunisation levels for other vaccine-preventable diseases. Or to put it another way, when rates of routine vaccination—children receiving all their shots on schedule, as a preventive measure rather than a reaction to an outbreak—start to fall, or is not high enough, the first sign is usually a measles outbreak. In global-health security terms, such outbreaks are the proverbial canaries in the coal mine.

A nurse at Merawi health centre in northern Ethiopia prepares a measles vaccine for delivery. Photo: Pete Lewis / DFID (CC BY 2.0)

What this means is that if we can prevent measles outbreaks it will have implications well beyond just one disease. Since 2000 there has been significant progress made towards this end. The annual number of measles deaths has fallen from 700,000 and, compared with a scenario of no measles vaccination, more than 20 million lives are estimated to have been saved during this period, thanks largely to a global push by the World Health Organization to eliminate measles. And this year we saw the Region of the Americas declared as measles-free.

So, why then are we now seeing an increase? The fact is, over the last six years progress has stagnated. Today 20 million children are still missing out on measles vaccination in their first year of life and, as a result, hundreds of children still die of the disease every day. One reason for this is that elimination efforts have often relied on region-by-region mass measles vaccination campaigns. These campaigns are often too reactive to be effective over the long term, treating the symptom of a measles outbreak rather than the broader cause: a lack of intensive efforts to improve routine immunisations.

Measles vaccination campaign. Tanzania, 2014. Photo: Gavi / Karel Prinsloo

While mass vaccination against a single disease is certainly an effective tool with which to prevent and respond to outbreaks, frequent mass vaccinations can also draw attention and resources away from more long-term efforts to increase routine immunisation coverage. As a result, it can inadvertently increase the risk of future outbreaks of measles and other infectious diseases if not planned well. To avoid this a different approach is needed, one which involves focussing resources on routine immunisation to boost population immunity against multiple diseases, rather than playing catch-up with just one, and then complemented by well-planned mass vaccinations.

This time last year my organisation Gavi, the Vaccine Alliance, approved a comprehensive new measles strategy aimed at precisely this. While it may not have come in time to make a dent in these latest mortality figures, our hope is that in the coming years it will help to break the stagnation, so that we finally start to see the numbers come down once again.