Laboratory-confirmed invasive meningococcal disease: effect of the Hajj vaccination policy, Saudi Arabia, 1995 to 2011.

Saudi Arabia (SA) experienced two large invasive meningococcal disease (IMD) outbreaks during the 2000 and 2001 Hajj pilgrimages. In 2002, polysaccharide quadrivalent ACWY vaccines became mandatory for Mecca and Medina pilgrims/residents older than two years. This study aimed to analyse IMD surveillance data among citizens, residents and pilgrims in SA from 1995 to 2011, focusing on changes before and after the new vaccination policy. For all laboratory-confirmed IMD cases in the national surveillance database from 1995 to 2011, serogroup and age were retrieved. The cases' seasonal distribution as well as the case fatality ratios (CFR) were obtained. For Saudi citizens/residents and Hajj pilgrims, annual rates were calculated using mid-year population estimates. The Student's t-test was used to compare means between the pre-epidemic (1995-1999) and post-epidemic (2002-2011) periods, excluding outbreak years. From 1995 to 2011, laboratories notified 1,103 cases. Between the pre- and post-epidemic periods, mean annual IMD rates decreased from 0.20 (standard deviation (SD): 0.1) to 0.06 cases/100,000 (SD: 0.06; p=0.02), mean numbers of Hajj-related cases from 13 (SD: 9.3) to 2 cases/year (SD: 2.3; p=0.02) and the mean age from 31 (SD: 1.3) to 18 years (SD: 1.4; p<0.01). The CFR in Saudi citizens (10.4) was lower than among foreign pilgrims (28.9) and decreased from 19.3% (SD: 1.8) in the pre-epidemic to 11.4% (SD: 7.0; p=0.04) in the post-epidemic phase. The decrease of annual IMD rates, CFR and Hajj-related cases between the pre- and post- vaccine era suggests a possible positive effect of the mandatory ACWY vaccination for pilgrims/residents in Mecca and Medina. Regular surveillance with an annual data analysis is necessary to monitor trends and circulating serotypes and to implement appropriate public health measures to avoid new IMD epidemics during upcoming Hajj seasons.