Do we really need a new measles vaccine?

Measles, that deadly childhood infectious disease is almost a distant memory to most people nowadays, that is except for a few isolated outbreaks across the US and Europe. This is all because of a really amazing preventative therapy: the vaccine.

Vaccines are great. They are by far the most effective means that we have to control - and hopefully eradicate - infectious diseases from a range of species. Measles is one of these diseases that, over the last half a decade or so, we have backed into a corner across the world. Before the introduction of global immunisation the measles virus caused around 2.6 million deaths, most of which were children. To show just how great the vaccine is: 2008 saw only 164,000 deaths (see the WHO data here). A big number still but a 97% decrease in associated fatalities is pretty impressive, so why then - in an editorial piece in the esteemed journal Vaccine, are they calling for researchers to develop a new vaccine?

For some viruses and bacteria, such as polio and whooping cough, our developed vaccines work very well. For others, like HIV and hepatitis C, they don't work well at all. It has always been thought that measles was quite the opposite but if you look at the current figures (some of which are shown below) you begin to see a worrying trend - a trend that was perhaps hidden amongst the sheer number of people infected by the virus. This trend suggests that if we don't change our vaccine, we may never be able to eradicate - or even truly control - measles.

Measles data from the Vaccine article. Notice even those vaccinated may still get the disease.

This may not be such a surprise to some of you who are aware of the difficulties in trying to vaccinate large numbers of children in some of the world's most difficult to live-in places, places like the Democratic Republic of Congo and Papua New Guinea. But a number of the measles epidemics are occurring in countries with much more developed health and public infrastructure. For example, in the last few months the U.S experienced 15 such outbreaks, the most ever seen for over 15 years. Why then in countries that can afford to give their children two doses of the measles vaccine are we seeing eruptions of disease?

This could be attributed to a number of things, not only the quality of our vaccine. And one issue is clearly logistical factors: people are simply not getting the vaccine due to unsubstantiated health scares for example. This however does not explain why people with two doses are getting the disease. The worrying thing that the Vaccine editors are concerned about is that maybe our vaccine, which we have used for nearly 50 years and developed by the famous John Enders, is not all that good after all.

Vaccine failure is not a new problem. Readers of this blog will even recognise these fears from a number of posts I have done on the recent re-emergence of mumps across the developed world. Vaccines fail by a) failing to produce an immune response in a patient and b) even after generating appropriate immunity, for some reason this can't protect against the virus. We call these primary and secondary failures, respectively. 

To illustrate this point: it is known that following administration our measles vaccine can - in some people - not even be recognised by their immune system and in others, if we go back an revisit them a number of years after immunisation, the will not have enough antibodies in their system to stop the virus in it's tracks. Another roadblock for us is our inability to protect very young children from the disease. The presence of maternal antibodies, transferred to the newborn following birth can sometimes fail to both protect against disease and even works against the vaccine and stops it working. The worrying thing is that at a population level, we need at least 95% percent of all people to be immune to measles if we are to have any chance of eliminating the virus from the human species by inducing herd immunity. Even a small number of failures can cause a big problem for us.

John Enders who developed the original (and still used in the MMT) measles vaccine. Will his vaccine continue to work?

So if it seems that our vaccine isn't up to the job, what are we to do? Is a new improved vaccine - one that may take years to develop and millions of pounds in funding to generate - the way forward? What do we do if we can't get the vaccine to everybody and even when we do it doesn't work in the first place and then even if it does it won't do so for very long. Ideally we would like a cheap, safe, stable vaccine that can be given once to children shortly after birth that will protect against the virus in everyone vaccinated for the rest of their lives and could be given by untrained people. But is this an impossible dream?

For one of the problems, the loss of protection over time, we may be able to get around it by simply giving a third dose later in life, but for the other issues we will need to do something better. And what this article has done is capture the health, economic and scientific need to generate a new and improved vaccine. This is why over the last few years there have been a number of projects looking into how we can improve on history and quickly get the next generation of vaccine technology up and running: whether that be giving the vaccine in aerosol 'mist' form; generating a solely DNA-based vaccine; or even through making our vaccines more heat-stable. The aim is that once these have been tested we will be able to role them out across the world and will eventually remove measles from the population. They will also provide a backdrop that will allow us to produce better vaccines for other hard to treat pathogens.

Poland GA, & Jacobson RM (2012). The re-emergence of measles in developed countries: Time to develop the next-generation measles vaccines? Vaccine, 30 (2), 103-4 PMID: 22196079


 

Related posts from this blog:

• The grand challenge of Aerosolised vaccines.
• Improving global immunisation with more heat tolerant vaccines.
• Measles, Papua New Guinea and the brain.
• A mothers love declines - a measles vaccine problem.