The recent outbreaks of bacterial meningococcal disease in England and New Zealand have brought attention to this severe and life-threatening illness. Meningitis and blood poisoning (septicaemia) are the two primary manifestations of the disease, caused by the bacterium Neisseria meningitidis. While other infectious agents can also cause these conditions, bacterial meningococcal disease is the most severe form, particularly affecting infants, children, and young adults. The disease's high risk in these demographics underscores the urgency of vaccination efforts.
The Neisseria meningitidis bacterium has several strains, with most belonging to six groups: A, B, C, W, X, and Y. These strains possess an extraordinary ability to swap genetic material and switch genes on and off through phase variation, enabling them to evade the body's immune system. This adaptability is a significant concern, especially for the Group B meningococci strains responsible for the recent outbreaks in both countries.
The Bexsero vaccine, designed to protect against bacterial meningitis caused by Group B strains, is a crucial tool in the fight against this disease. It recognizes components in the outer membrane and on the surface of the bacteria, making it effective against the UK outbreak strain, which matches one of the protein antigen sequences used in the vaccine. However, the genomic sequencing of bacteria responsible for some cases in New Zealand is still pending, highlighting the ongoing challenges in understanding and combating this disease.
Genome sequencing plays a vital role in distinguishing between outbreaks and scattered cases. It helps determine if an outbreak is due to a specific strain or a cluster of genetically unrelated cases. Past genomic surveillance in New Zealand has revealed the emergence of outbreak strains and identified antibiotic resistance. For instance, a W group strain variant caused a rise in meningococcal disease between 2016 and 2019, with increased resistance to penicillin.
Interestingly, the bacterium causing meningococcal disease can often be found in people's throats without causing symptoms, making them carriers. About 5% to 30% of the global population are carriers, and most don't experience any symptoms or disease. Genome sequencing has shown that some highly virulent strains associated with outbreaks are rarely identified in samples from healthy carriers, but the reasons for this remain inconclusive.
The likelihood of carrying the bacterium varies with age, being low in younger children and older people but high in teenagers and young adults. This high carriage rate in young adults, especially university students, exacerbates the risk of developing the disease. In New Zealand, both the Bexsero and MenQuadfi vaccines are available to young people entering boarding school or university, while in England, only the MenQuadfi vaccine is currently funded for university students.
The impact of COVID measures on disease transmission is another critical aspect. Lockdowns and border controls reduced the spread of the SARS-CoV2 virus but also affected other diseases, including influenza and respiratory viruses. Meningococcal disease cases were significantly reduced during the COVID response, likely due to decreased contact between individuals and fewer infected people entering the country. However, the expected rebound in cases following the relaxation of these measures emphasizes the ongoing need for vigilance and vaccination.
In conclusion, the recent outbreaks of bacterial meningococcal disease highlight the importance of vaccination and genomic surveillance. The disease's severe nature, particularly in young adults, and its ability to adapt and evade the immune system make it a significant public health concern. By understanding the strains, carriers, and transmission dynamics, we can better prepare and protect ourselves against this life-threatening illness.
