Lack of serum bactericidal activity in preschool children two years after a single dose of serogroup C meningococcal polysaccharide-protein conjugate vaccine.

BACKGROUND: There is an increased risk of invasive meningococcal disease during the teenage years. A cohort of children vaccinated with a single dose of meningococcal C protein-polysaccharide conjugate (MenC) vaccine in early childhood during the U.K. catch up campaign will enter this age group during the coming decade. The duration of protective immunity against invasive meningococcal C disease provided by this single dose regimen is uncertain.A serum bactericidal titer of <1/8 correlates with susceptibility to invasive meningococcal disease. We assessed this correlate of protection in a cohort of children approximately 2 years after a single dose of vaccine. METHODS: Serum bactericidal activity was assessed in 94 children (median age, 4.0 years) at a median time of 1.8 years after vaccination. RESULTS: Of the 94 children, 59 (63%) had a serum bactericidal titer