The Return of MenW: Religious Mass Gatherings as Global Catalysts for Meningococcal Spread

Abstract

Between January 2024 and June 2025, England has reported a concerning rise in invasive meningococcal disease (IMD) caused by Neisseria meningitidis serogroup W, particularly the ‘strain A’ of the MenW: cc11 Hajj sublineage—closely associated with pilgrimage travel to Saudi Arabia [1]. Several of these cases were linked to Umrah pilgrims and their close contacts, underscoring the persistent public health risks posed by mass gatherings such as Hajj and Umrah [1]. Reinforcing MenACWY vaccination messaging year-round—especially for intending pilgrims—remains a critical strategy to mitigate this emerging threat. A recent systematic review of 21 studies involving 23,552 participants (nine included in meta-analysis) found that meningococcal carriage patterns shift during the Hajj period [2]. Carriage of serogroup A remained extremely low both before (0.003; 95% CI: −0.001 to 0.006) and after Hajj (0.001; 95% CI: 0.000 to 0.002). In contrast, serogroup W carriage increased slightly from 0.068 (95% CI: −0.014 to 0.15) pre-Hajj to 0.072 (95% CI: 0.037 to 0.108) post-Hajj. Overall N. meningitidis carriage rose from 1.6% before Hajj to 3.4% afterward [2]. Recent data from England show that 32 of 59 MenW IMD cases were associated with travel-related strains, nearly half of which were directly linked to returnees from Saudi Arabia [1]. The dominant strain, belonging to the highly virulent MenW: cc11 clonal complex, is well recognized for triggering outbreaks in settings characterized by large crowds and close contact, such as the annual Hajj pilgrimage [3,4,5]. This clear epidemiological connection underscores both the global mobility of the strain and the critical need for sustained surveillance and preventive measures targeting pilgrims and their households.

Keywords: Hajj, Umra, Saudi Arabia, Religious, Meningococcal vaccine