France recorded ‘post-COVID’ surge in meningococcal disease

An unprecedented resurgence in invasive meningococcal disease followed the lifting of pandemic restrictions in France, according to a paper published in the Journal of Infection and Public Health by scientists from the Institut Pasteur. The team used data from the National Reference Center for Meningococci to trace the evolution of invasive meningococcal disease cases in France between 2015 and 2022, revealing the striking trend.

Respiratory infections fell across the board when hygiene measures and social distancing were introduced to combat COVID-19. The number of invasive meningococcal disease (IMD) infections fell by more than 75% in 2020 and 2021.

‘During the COVID-19 pandemic, two theories emerged,’ explained Dr Muhamed-Kheir Taha, Director of the National Reference Centre for Meningococci at the Institut Pasteur. ‘The first was that this positive effect would last and that meningococci would stop circulating over the long term. The second was that there would be a rapid resurgence in bacterial activity among a naive population which had not come into contact with the bacteria for a long time.’

It is now clear that the second hypothesis was correct. ‘There was an unprecedented resurgence in invasive meningococcal disease in autumn 2022, and in autumn 2023, the number of cases was higher than in the pre-COVID-19 period,’ said Samy Taha, a scientist in Pasteur’s Invasive Bacterial Infections Unit.

Compared with a total of 298 cases recorded between January and September 2019, 421 cases were recorded between January and September 2023 – a rise of 36%, even though the winter peak had not arrived. The figure for the same period in 2021 was 53 cases.

There are two main explanations for this: general immunity was weaker because strains were circulating less, but there was also a decrease in vaccination, with meningitis C vaccination falling by 20% during the first lockdown, for example. So, the population has become naive when faced 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 with the other serogroups,’ said Dr Ala-Eddine Deghmane, Deputy Director of the National Reference Centre for Meningococci at the Institut 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 meningococcal bacterial strains responsible for IMD today are different from those that were circulating before the pandemic, and they target different age groups. ‘It is almost as if the COVID-19 epidemic has reset the entire system,’ said Samy Taha.

This resurgence in meningitis could gather momentum in the coming months with the effect of seasonal influenza. The influenza virus creates a favorable context for the development of meningococcal bacteria. All mass gatherings can be a risk factor for infection in general, and especially for IMD.

In France, only meningitis C vaccination is mandatory; vaccination for meningitis B is merely recommended in infants. But there are not yet any recommendations in the general population for serogroups Y and W.

The scientists are in contact with the French National Authority for Health to help adapt the future vaccine strategy. ‘If the quadrivalent meningococcal vaccine for serogroups A, C, Y and W were to be recommended for adolescents, it would provide direct protection for them and also indirect protection for other categories of the population,’ said Ala-Eddine Deghmane.

Adolescents are the main healthy carriers of meningococci. ‘We must remember that without treatment, the mortality rate for bacterial meningitis is virtually 100%. Even with proper treatment, there is still a 10% mortality rate. So, vaccine prevention is crucial,’ concluded Muhamed-Kheir Taha.