Looking at the back of the throat to help understand a serious cause of meningitis
Headed by Professor Martin Maiden, the study is investigating what proportion of teenagers in the UK carry meningococcal bacteria (Neisseria meningitidis), and what the risk factors are in this age group. Six different types of the bacteria (MenA, B, C, W, X and Y) cause meningococcal disease, a very serious illness that can result in meningitis, septicaemia and death, with survivors often suffering major long-term effects such as amputations or brain damage. The study may have an impact on the deployment of vaccines against the disease.
There are many unanswered questions about Neisseria meningitidis and its ability to cause disease. In the vast majority of people – up to 10 per cent of adults and 25 per cent of teenagers at any one time – the bacteria live harmlessly at the back of the throat without causing any symptoms. They come and go, and can be passed from person to person. It is not understood why, in a small number of cases, the bacteria break through the body’s natural defences and cause serious invasive disease. Very unusually for infectious diseases, teenagers are at greater risk of meningococcal disease than any other age group except the under 5s, and the reasons for this are not entirely clear. Nor is it understood why there are fluctuations in the number of disease cases over time: 15 years ago rates of disease were high, for example, whereas at the moment rates are much lower.
The UK Meningococcal Carriage Study is perfectly positioned to help find the answers to some of these questions. It is the fourth study of its kind to be run by Professor Maiden over the last 16 years, and the vast amount of data collected is enabling the team to build up a detailed picture of the state of Neisseria meningitidis across the UK since 1999. Over the past few months throat swabs have been taken from over 21,000 16 to 19 year olds across the country, including here in Oxford. This represents more than one per cent of this age group in the UK – a very large sample indeed. Teenagers have also been asked to complete a questionnaire about lifestyle factors, as it is thought that changes in behaviour may be the cause of the increased level of risk in this age group.
One key impact of the research is to support the introduction of vaccines into the UK immunisation schedule. Common sense might suggest that it is best to vaccinate the groups who are most affected by the disease – in other words babies and young children. But earlier carriage studies conducted around the time that a vaccine against type C of the disease (MenC) was introduced in the UK showed conclusively that the vaccine had a ‘herd immunity’ effect; by reducing the number of bacteria circulating in the population as a whole, it indirectly protected those who had not been vaccinated. This was unexpected, and demonstrated that the most effective target group for the MenC vaccine was in fact likely to be teenagers, precisely because they are the main carriers of the bacteria. By reducing carriage in that group, you effectively reduce transmission to other vulnerable groups. The UK vaccination schedule has been gradually modified to accommodate this finding; from initially offering doses of the MenC vaccine at three, four and 13 months, the schedule now recommends doses at three and 13 months, followed by a third dose at 13-14 years of age.
This new carriage study comes at a very important time for meningococcal disease in the UK. Disease caused by the MenC strain has almost disappeared as a result of the MenC vaccine introduced in 1999, but there are still several hundred cases of MenB disease every year in the UK, and recently there has been an alarming rise in the number of cases of MenW disease. Over the next few months, while the data from this study is being analysed, vaccines to combat MenB and MenW will be introduced into the routine NHS schedule. The study is therefore poised to give a unique picture of meningococcal carriage just before new vaccines start to affect the pattern of disease.