Meningococcal Disease: Outbreaks in England and New Zealand Trigger Research and Vaccination Calls
Outbreaks of bacterial meningococcal disease have been reported in England and among students in New Zealand, highlighting concerns about this severe illness.
The disease is caused by the bacterium Neisseria meningitidis, manifesting as meningitis (inflammation of the membranes covering the brain and spinal cord) or septicaemia (blood poisoning). While other infectious agents can cause similar conditions, bacterial meningococcal disease is considered the most severe form. Infants, children, and young adults are identified as higher-risk groups.
Ongoing research aims to compare the meningococcal strains involved in both countries and to understand the role of asymptomatic carriers. Neisseria meningitidis comprises several strains, predominantly categorized into six groups (A, B, C, W, X, Y). These bacteria possess the ability to exchange genetic material and alter their surface characteristics, which enables them to evade the body's immune system.
The strains responsible for the UK outbreak and the recent cases in Dunedin, New Zealand, both belong to Group B meningococci. However, the UK outbreak strain is identified as ST485, whereas the Dunedin cases involved different strains that varied from the UK strain and from each other, indicating multiple transmission chains.
The Bexsero vaccine is used to provide protection against Group B meningococcal disease by targeting components in the outer membrane and on the bacterial surface. The strain linked to the UK outbreak is likely covered by the Bexsero vaccine due to a match in protein antigen sequences. Genomic sequencing for one Dunedin case is pending, and bacterial culture was not obtained for another case.
Importance of Genome Sequencing
Strain typing and genome sequencing are vital tools for determining whether an apparent outbreak is caused by the emergence of a specific strain or by a cluster of genetically unrelated cases.
Both scenarios can arise when cases share common risk factors, such as increased close contact in educational settings. Previous genomic surveillance in New Zealand has identified the emergence of outbreak strains and helped detect likely antibiotic resistance. For instance, a W group strain variant caused a rise in meningococcal disease cases between 2016 and 2019 in New Zealand and demonstrated increased resistance to penicillin.
Healthy Carriers and Risk Factors
Despite its potential to cause severe disease, Neisseria meningitidis is frequently found in the throats of asymptomatic individuals. An estimated 5% to 30% of the global population are carriers without experiencing symptoms or disease. The precise factors determining whether disease develops in carriers are not fully understood. Genome sequencing has shown that some highly virulent strains associated with outbreaks are rarely found in samples from healthy carriers, but genomic explanations for differences between bacteria found in outbreaks and healthy carriers remain inconclusive.
The likelihood of carrying the bacterium is age-dependent, being lower in younger children and older individuals, but higher in teenagers and young adults. The high carriage rate in young adults, coupled with crowded living conditions, makes university students a high-risk group for developing the disease.
In New Zealand, both the Bexsero (against Group B) and MenQuadfi (against ACWY) vaccines are available for young people entering boarding school or university halls. In contrast, only one vaccine (against ACWY) is currently funded for university students in England. Maximum protection requires both vaccines; conjugate ACWY vaccines may reduce carriage and transmission, while Bexsero primarily protects against the development of the disease.
Impact of COVID-19 Measures
COVID-19 lockdowns and border controls reduced the transmission of SARS-CoV2 and other diseases, including influenza and meningococcal disease.
A rebound in meningococcal disease cases following the relaxation of these strict measures was anticipated.
This underscores the importance of public awareness regarding risks associated with large gatherings, particularly among young people, and the need for vaccination with the Bexsero vaccine as part of the immunization schedule, alongside MenQuadfi for high-risk groups.