Meningococcal cases tracked Umrah as pilgrim vaccination compliance fell to 54%

The World Health Organization reported 11 confirmed cases of invasive meningococcal disease in early 2025, all in people who had performed Umrah in Saudi Arabia between 7 January and 12 March [s1]. A modelling study published in August puts a number on what those cases could become if vaccination among pilgrims continues to slip [s2].

What WHO reported

The 11 confirmed cases were notified to WHO on 13 March 2025 [s1]. Four were reported from three countries in the WHO Eastern Mediterranean Region and the remainder from people with travel history to countries in the South-East Asia Region [s1]. The median age was 36 years, with a range of 6 to 69, and 64% were male [s1]. None of the affected individuals had a history of meningococcal vaccination [s1]. All were treated in hospitals in Saudi Arabia, recovered and were discharged [s1]. Serogrouping identified the causative strain as Neisseria meningitidis serogroup W135 [s1].

A further six isolated cases were reported between 11 February and 18 March 2025 among people recently returned from Umrah — three from the WHO European Region and three from the Eastern Mediterranean Region, with a median age of 19 [s1]. Serogroup W135 was confirmed in two of those six [s1].

WHO also recorded a pattern in the preceding year. In 2024, 12 cases of meningococcal disease associated with pilgrimage to Saudi Arabia were reported from the United States, the United Kingdom and France [s1]. Nine of those patients were unvaccinated and the status of the other three was unknown [s1]. Antimicrobial susceptibility data were available for 11 of the 12, and ciprofloxacin-resistant strains were identified in three [s1]. That resistance matters because ciprofloxacin is used for post-exposure prophylaxis of contacts.

The vaccination gap

Quadrivalent meningococcal vaccination — MenACWY, covering serogroups A, C, W and Y — has been mandatory for pilgrims travelling to Saudi Arabia for Hajj and Umrah, a requirement WHO describes as in place since 2001 [s1]. WHO states that these measures have mitigated the risk of pilgrimage-associated outbreaks [s1].

Compliance, however, has fallen. As of 10 March 2025, Saudi health authorities estimated that only 54% of international Umrah pilgrims had complied with the meningococcal vaccination requirement [s1]. WHO notes that vaccination compliance for Umrah had declined over the previous two years [s1]. Because returning travellers can carry the bacterium to their home communities, lower compliance raises the risk not only for pilgrims but for the wider population [s1].

The scale of the exposure is large. WHO cited an estimate that 24 million pilgrims performed Umrah in 2024, half of them international [s1]. Umrah is a year-round pilgrimage, so the exposure is not confined to a single season [s1].

What the model estimates

The modelling study, published in Infectious Diseases and Therapy on 28 August 2026, extended an existing meta-population model of N. meningitidis transmission during Hajj to include Umrah [s2]. The model divided the population into pilgrimage-site residents, the broader Saudi population, and non-Saudi populations from high-, medium- and low-transmission settings, and was calibrated with data from 1995 to 2011 and validated against 2012 to 2024 [s2]. The work was conducted by authors affiliated with the vaccine manufacturer Sanofi, a point readers should weigh when assessing a study whose conclusion favours wider vaccination [s2].

The model found that Umrah accounted for roughly 90% of pilgrimage days in 2023–2024, with external pilgrims making up more than 90% of those days [s2]. Under a scenario in which external pilgrim numbers rise in line with the Saudi Vision 2030 target of 30 million external Umrah pilgrims a year by 2030, the estimated probability of more than 100 annual meningococcal cases among pilgrims over 2025–2034 was 53% if vaccination coverage among internal and external Umrah pilgrims stayed at 10% [s2]. At 90% coverage for both groups, that probability fell to below 0.02% [s2].

The model also estimated that 90% coverage would reduce the expected number of cases across Saudi Arabia by more than 80% compared with no vaccination [s2].

The limits

A model is a set of assumptions, not a measurement. Its outputs depend on the transmission parameters carried over from the earlier Hajj model and on the projected growth in pilgrim numbers, and the authors' affiliation is a relevant caveat [s2]. The WHO report, by contrast, describes confirmed cases but cannot establish how many infections went undetected [s1]. What the two sources share is a direction: a documented decline in vaccination compliance, a serogroup W135 signal in recent cases, and a modelled relationship in which coverage is the variable that most changes the outcome [s1][s2].

WHO does not recommend any restriction on travel to or trade with Saudi Arabia on the basis of the reported cases [s1].