Meningococcal Group W (MenW)
Meningococcal W meningitis and septicaemia: a new, virulent strain
- Cases of meningococcal W disease are rising steeply
- Our genome library has identified the rise is due to a particularly virulent ST-11 strain
- The ST-11 strain is causing severe disease in healthy teenagers and young adults
- This strain is more deadly with a higher than usual death rate of 13%
- These cases often have different symptoms to other kinds of meningococcal disease
- All 14-18 year olds are to be offered MenACWY vaccine by late summer 2017 to prevent further increases in disease amongst the wider population
- From September 2015 MenACWY vaccine is replaced the MenC booster for 14 year olds.
- Babies will not be immunised with ACWY, but the MenB vaccine, Bexsero, would provide protection against this ST-11 strain
Meningococcal infection has always been the leading cause of meningitis in the UK. Six different kinds, serogroups A, B, C, W, X, and Y cause the most disease. For decades meningococcal B has been the main serogroup, and meningococcal C was also common until the MenC vaccine was introduced, reducing cases to just a handful each year.
However, cases of meningococcal W (MenW) have risen year on year since 2009. Public Health England has shown that since 2008/9 when MenW accounted for only 1-2% of meningococcal cases, it has increased to cause 24% of cases in 2014/15.
Our meningococcal genome library
has played a vital part in helping Public Health England to stay a step ahead of the game in the fight against meningococcal disease. Analysis of MenW isolates in the genome library has revealed that almost all of the increase in MenW disease is attributable to a particularly virulent type of meningococcal bacteria called ST-111
The rise in this ST-11 MenW disease is particularly alarming because it is striking mainly healthy people across all age groups, with a marked spike amongst teenagers (figure 1) and cases are rising steeply. 34 cases were reported in January 2015 compared with 18 and 9 for the same time period over the previous two years2
The ST-11 strain is associated with severe illness which often requires treatment in intensive care and has a higher associated death rate than other strains of meningococcal disease, (13% case fatality compared to 5-10%) 1
It often has different symptoms to other kinds of meningococcal disease:
- Rather than meningitis or septicaemia, some people with MenW infection may get septic arthritis or a severe respiratory tract infection, such as pneumonia, epiglottitis or supraglottitis (in these latter two conditions there is a dangerous swelling around the "lid" that covers the windpipe , blocking the flow of air into the lungs).
- Several adults with MenW septicaemia have had mainly gastrointestinal symptoms but without the characteristic non-blanching rash and progressed rapidly to death.
This is the same strain that has been causing epidemic disease in Argentina, Brazil and in Chile, where it is associated with a death rate of 28%3
compared to 10% for other strains in the country.
Figure 1:Number of laboratory confirmed cases of MenW disease and associated deaths by age group and year of diagnosis over six epidemiological years in England and Wales. Source1
As a direct result of this information, the government’s vaccine advisers, the Joint Committee on Vaccination and Immunisation (JCVI) have advised that 14 to 18 year olds should be immunised with ACWY vaccine as soon as possible to prevent rapid increases in disease amongst the rest of the population4
. The Department of Health has accepted the JCVI’s advice and is currently planning the implementation of a combined ACWY immunisation programme in this age group5
. How will the vaccination of 14 to 18 year olds protect the wider population?
Adolescents aged between 14 to 18 are more likely to carry meningococcal bacteria than any other age group and offering ACWY vaccine to all of them should stop the bacteria from being passed on. This means that even unvaccinated people will be protected from catching the disease – an effect known as herd protection.
Although we welcome the implementation of the ACWY vaccine amongst 14-18 year olds, it will take over a year for herd protection to establish so babies (who are particularly vulnerable to developing disease) will remain unprotected. However, it has been shown that the MenB vaccine Bexsero, to be brought in for children at 2, 4 and 12 months in the UK, would protect against this ST-11 MenW strain6
. More about the MenB vaccineMeningococcal group W disease around the world
- Shamez N. Ladhani, et al. Increase in endemic Neisseria meningitidis capsular group W ST-11 complex associated with severe invasive disease in England and Wales. Clinical Infectious Diseases 2014 [cited Advance access November 10]; Available here
- Public Health England, Health Protection Report. Volume 9 Number 7. Continuing increase in meningococcal group W (MenW) disease in England. Published on: 27 February 2015. Available here
- XIXth International Pathogenic Neisseria Conference (IPNC). IPNC Abstract 2014 - Oral Abstract O16 2014; Available here
- Joint Committe on Vaccination and Immunisation. Minute of the meeting on 4 February 2015. 2015 [cited 2015 March]; Available from here
- Public Health England. Press release: Meningococcal group W (MenW) immunisation advised for 14 to 18 year-olds. 2015 [cited 2015 13 March]; Available from here
- XIXth International Pathogenic Neisseria Conference (IPNC). IPNC Abstract 2014 - Poster Abstract P30 2014; Available here
What is MenW ST-11?
Meningococcal bacteria are classified according to structural differences in certain components. The serogroup, e.g. A, B, C, W or Y, is defined by the type of sugar coat, or capsule, that surrounds the bacteria.
Meningococcal bacteria can also be classified according to certain parts of their genetic make-up. This type of classification is known as Multi Locus Sequence Typing (MLST) and it is based on similarities between seven ‘housekeeping’ genes within the meningococcal genome. The advantages of classifying bacteria in this way is that it can provide information about how bacteria are evolving over time and the information can easily be shared between laboratories and researchers1
. This is one of the reasons why our genome library is such a useful resource.
Genetic sequences which are identical across the seven housekeeping genes will belong to a given sequence type (ST). Meningococcal bacteria belonging to ST-11 have been identified as especially virulent and have been associated with outbreaks that particularly affect healthy people in their prime, namely teenagers and young adults.
- Maiden, M.C., et al., Multilocus sequence typing: A portable approach to the identification of clones within populations of pathogenic microorganisms. Proc Natl Acad Sci U S A, 1998. 95(6): p. 3140-5.
Page last updated 19.08.16