Haemophilus influenzae Type b Meningitis in the Short Period after Vaccination: A Reminder of the Phenomenon of Apparent Vaccine Failure

We present two cases of bacterial meningitis caused by Haemophilus influenzae type b (Hib) which developed a few days after conjugate Hib vaccination. This phenomenon of postimmunization provocative time period is reviewed and discussed. These cases serve as a reminder to clinicians of the risk, albeit rare, of invasive Hib disease in the short period after successful immunization. 1. Introduction Haemophilus influenzae type b (Hib) was the leading cause of bacterial meningitis in children worldwide until the introduction of the Hib conjugate vaccine in the early 1990s [1]. Since then, the incidence of Hib disease has declined dramatically in high-income countries and virtually eliminated in parts of the United States and Europe [1]. In 1994, the Hib-conjugated vaccine was introduced into the Israeli National Immunization Program. In 1997, a four-dose vaccine schedule was adopted, given at 2, 4, 6, and 12 months of age. Prospective surveillance estimated that vaccine effectiveness was 95% (95% CI 92–96%) against any invasive disease and 97% (95% CI 93–98%) against bacterial meningitis [2]. Nevertheless, over the past 20 years, there have been some reports of invasive Hib disease within a short period after administration of the vaccine [3–5]. This report describes two children in whom Hib meningitis developed a few days after vaccination. These cases serve as a reminder for clinicians of a phenomenon of elevated risk for infection and apparent vaccine failure in the short period after Hib immunization. 2. Case Reports 2.1. Case 1 A 10-week-old girl presented to another hospital with fever, refusal to eat, grunting respirations, and hypertonicity of 48-hour duration. All symptoms began one day after she had received the first dose of the combination Infanrix-IPV+Hib vaccine (a combined vaccine against diphtheria, tetanus, pertussis, polio, and Hib infections). Her parents reported that she had been perfectly healthy the day before vaccination. Past medical history revealed that the patient had been born at 31 weeks’ gestation after premature rupture of the membranes; maternal fever was documented during delivery. She was hospitalized in the neonatal intensive care unit and treated with empiric antibiotics for 3 days pending blood culture results. The rest of her hospitalization was uneventful, and she was discharged at the age of 5 weeks in good medical condition. At the present admission to the other hospital, bacterial meningitis was suspected on the basis of abnormal cerebrospinal fluid (CSF) cell count (2358/mm3, with neutrophil predominance 60%),