Objectives Bacterial meningitis is associated with high mortality and long-term complications. This study assessed
the impact of Haemophilus influenzae type b (Hib) conjugate vaccine on childhood bacterial meningitis in
Ulaanbaatar, Mongolia.
Study design Prospective, active, population-based surveillance for suspected meningitis in children aged 2-59
months was conducted (February 2002-January 2011) in 6 hospitals. Clinical data, blood, and cerebrospinal fluid
were collected. The impact of Hib conjugate vaccine was assessed by comparing Hib and all cause meningitis
data in the 3 years preceding pentavalent conjugate vaccine implementation (2002-2004) with 3 years postimplementation
(2008-2010).
Results Five hundred eleven cases of suspected meningitis were identified from 2002-2011. Pentavalent conjugate
vaccine coverage in December 2005 in Ulaanbaatar city was 97%. The proportion of suspected cases con-
firmed as Hib meningitis decreased from 25% (50/201) in the prevaccination era to 2% (4/193) in the
postvaccination era (P < .0001). The annual incidence of Hib decreased from 28 cases per 100 000 children in
2002-2005 to 2 per 100 000 in 2008-2010 (P < .0001).
Conclusions This article demonstrates the marked impact of Hib conjugate vaccine introduction on
meningitis in Mongolia. It is important to sustain this surveillance system to monitor the long-term impact
of Hib conjugate vaccine, as well as other interventions such as pneumococcal and meningococcal vaccines.