OBJECTIVES: Collectively, the Hajj and Umrah pilgrimages draw >30 million pilgrims to the Kingdom of Saudi Arabia (KSA) each year. Before Hajj 2024 (14 to 19 June), the meningococcal serogroup W ST-11 complex (W:cc11) Hajj-strain sublineage caused multiple international cases of invasive meningococcal disease (IMD) associated with travel to the Middle East and Asia. Here we identify the strains responsible. METHODS: All Hajj strain sublineage genomes on PubMLST.org underwent core genome MLST comparisons (PubMLST.org). RESULTS: Isolates from 30 cases, across seven countries, formed five phylogenetic clusters within two distinct strains. Travel histories included KSA, other Middle Eastern countries, India, Mauritius, via Turkey, and no known associated travel. The prevalent strain, representing four clusters, had no African, and limited Middle Eastern, representation. The geo-temporal distribution of available genomes suggested Eastern Europe as a possible source. CONCLUSIONS: The rapid expansion of Umrah/travel-related W:cc11 IMD cases in early 2024 was due to multiple strains/sublineages. Despite the involvement of non-KSA travel-destinations, the coincidence of cases with the busy month of Ramadan, and the abrupt cessation during Hajj (when vaccine compliance is maximal), suggest that Umrah was a key driver and highlight the need to reinforce mandatory vaccination whilst maintaining global vigilance.

Invasive meningococcal disease (IMD), caused by infection with the bacterium Neisseria meningitidis, usually manifests as meningitis or septicemia and can be severe and life-threatening (1). Six serogroups (A, B, C, W, X, and Y) account for most cases (2). N. meningitidis is transmitted person-to-person via respiratory droplets and oropharyngeal secretions. Asymptomatic persons can carry N. meningitidis and transmit the bacteria to others, potentially causing illness among susceptible persons. Outbreaks can occur in conjunction with large gatherings (3,4). Vaccines are available to prevent meningococcal disease. Antibiotic prophylaxis for close contacts of infected persons is critical to preventing secondary cases (2).

BACKGROUND: Since the start of the 2009 influenza A pandemic (H1N1pdm), the World Health Organization and its member states have gathered information to characterize the clinical severity of H1N1pdm infection and to assist policy makers to determine risk groups for targeted control measures. METHODS AND FINDINGS: Data were collected on approximately 70,000 laboratory-confirmed hospitalized H1N1pdm patients, 9,700 patients admitted to intensive care units (ICUs), and 2,500 deaths reported between 1 April 2009 and 1 January 2010 from 19 countries or administrative regions-Argentina, Australia, Canada, Chile, China, France, Germany, Hong Kong SAR, Japan, Madagascar, Mexico, the Netherlands, New Zealand, Singapore, South Africa, Spain, Thailand, the United States, and the United Kingdom-to characterize and compare the distribution of risk factors among H1N1pdm patients at three levels of severity: hospitalizations, ICU admissions, and deaths. The median age of patients increased with severity of disease. The highest per capita risk of hospitalization was among patients <5 y and 5-14 y (relative risk [RR] = 3.3 and 3.2, respectively, compared to the general population), whereas the highest risk of death per capita was in the age groups 50-64 y and ≥65 y (RR = 1.5 and 1.6, respectively, compared to the general population). Similarly, the ratio of H1N1pdm deaths to hospitalizations increased with age and was the highest in the ≥65-y-old age group, indicating that while infection rates have been observed to be very low in the oldest age group, risk of death in those over the age of 64 y who became infected was higher than in younger groups. The proportion of H1N1pdm patients with one or more reported chronic conditions increased with severity (median = 31.1%, 52.3%, and 61.8% of hospitalized, ICU-admitted, and fatal H1N1pdm cases, respectively). With the exception of the risk factors asthma, pregnancy, and obesity, the proportion of patients with each risk factor increased with severity level. For all levels of severity, pregnant women in their third trimester consistently accounted for the majority of the total of pregnant women. Our findings suggest that morbid obesity might be a risk factor for ICU admission and fatal outcome (RR = 36.3). CONCLUSIONS: Our results demonstrate that risk factors for severe H1N1pdm infection are similar to those for seasonal influenza, with some notable differences, such as younger age groups and obesity, and reinforce the need to identify and protect groups at highest risk of severe outcomes. Please see later in the article for the Editors' Summary.