• Population: Immunocompetent children aged 3–9 months
• Intervention: Two doses of MenA conjugate vaccine (5 µg dosage)
• Comparison: No MenA vaccination
• Outcome: Serogroup A meningococcal disease

What is the scientific evidence concerning the efficacy of two doses of MenA conjugate vaccination (versus no Men A vaccination) against serogroup A meningococcal disease in immunocompetent children aged 3–9 months?