A team of scientists from the Institut Pasteur used the database of the National Meningococcal Reference Center to trace the evolution of cases of invasive meningococcal disease in France between 2015 and 2022, revealing an unprecedented resurgence of the disease after the relaxation of control measures imposed on the of the COVID-19 outbreak. The newly reported cases were mainly caused by meningococcal serogroups that were less common before the pandemic, and there was a particular increase in cases in people aged 16 to 24 years. The results, published in Journal of Infection and Public Health on October 12, 2023, should help adjust the vaccine strategy for this deadly disease.
During the COVID-19 outbreak, health and hygiene measures such as mask use and social distancing had a positive impact on respiratory infections. This was the case with invasive meningococcal disease (IMD), with the number of infections falling by more than 75% in 2020 and 2021. But what would happen at the end of the pandemic, when protective measures were relaxed?
During the COVID-19 pandemic, two theories emerged. The first was that this positive effect would last and that the meningococci would stop circulating in the long term. The second was that there would be a rapid resurgence of bacterial activity among a naïve population that had not been exposed to the bacteria for a long time.”
Muhamed-Kheir Taha, co-lead author of the study, Head of the Invasive Bacterial Infections Unit and Director of the National Reference Center for Meningococci at the Institut Pasteur
A group of scientists from the Institut Pasteur therefore decided to carry out a detailed study of the evolution of the disease between 2015 and 2022 and confirmed the second hypothesis.
Using samples from the National Meningococcal Reference Center, which has recorded all IMD cases in France since 1980, the scientists were able to go back to the period of the pandemic. The first observation was clear. “There was an unprecedented resurgence of invasive meningococcal disease in the fall of 2022, and now, in the fall of 2023, the number of cases is higher than in the pre-COVID-19 period,” describes Samy Taha, first author of the study and scientist. at the Invasive Bacterial Infections Unit of the Pasteur Institute. Compared to a total of 298 cases recorded between January and September 2019, 421 cases have already been recorded between January and September 2023 – a 36% increase, even though the winter peak has not yet arrived. The number for the same period in 2021 was 53 cases. There are two main explanations for this: overall immunity was weaker because strains were circulating less, but there was also a decline in vaccination, with meningitis C vaccination falling by 20% during the first lockdown, for example. Thus, the population has become naïve when dealing with bacteria that are constantly evolving – the bacterial genome is highly variable.
“Since the pandemic, there has been a particular resurgence in meningococcal serogroups W and Y compared to the other serogroups,” continues Ala-Eddine Deghmane, study co-leader and Deputy Director of the National Meningococcal Reference Center at the institute. Pasteur. “And although all age groups are concerned, we found that those most affected by this new wave of meningitis are young people aged 16 to 24.” In other words, the strains of meningococcal bacteria responsible for IMD today are different than those circulating before the pandemic and target different age groups. “It’s almost as if the COVID-19 epidemic has reset the whole system,” says Samy Taha.
This meningitis resurgence could gain momentum in the coming months with the impact of seasonal flu. The influenza virus creates a favorable environment for the development of meningococcal bacteria. All mass gatherings can be a risk factor for infection in general, and for IMD in particular.
In France, only the meningitis C vaccination is compulsory. Meningitis B vaccination is only recommended for infants. However, there are still no recommendations in the general population for serogroups Y and W. The scientists are therefore in contact with the French National Health Authority to help adapt the future vaccine strategy. “If the quadrivalent meningococcal vaccine for serogroups A, C, Y and W were recommended to adolescents, it would provide direct protection for them and also indirect protection for other categories of the population,” explains Ala-Eddine Deghmane. Teenagers are the main healthy carriers of meningococci. “We have to remember that without treatment, the fatality rate for bacterial meningitis is essentially 100%. Even with appropriate treatment, there is still a 10% mortality rate. Therefore, vaccine prevention is crucial,” concludes Muhamed-Kheir Taha.
Source:
Journal Reference:
Taha, S., et al. (2023). The rapid recovery of invasive meningococcal disease in France at the end of 2022. Journal of Infection and Public Health. doi.org/10.1016/j.jiph.2023.10.001.
