Risk factors The most frequently infected are Children aged 6 months to 3 years Other high-risk groups include Adolescents and young adults (16 to 20 years of age) Military recruits College freshmen living in dormitories Travelers to places where meningococcal disease is common (eg, certain countries in Africa and in Saudi Arabia during the Hajj) People with functional or anatomic asplenia or a complement deficiency People living with HIV infection People treated with eculizumab or ravulizumab Microbiologists working with N meningitidis isolates Close contacts of patients with invasive meningococcal disease Infection or vaccination confers serogroup-specific immunity.