Haemophilus influenzae type B primarily affects which age group?

• A. Adults over 65
• B. Children under 5
• C. Teenagers
• D. Newborns

Answer: (B)

This question tests understanding of which age group carries the highest risk for Haemophilus influenzae type B infection. Hib disease has historically caused serious invasive illness like meningitis mainly in young children. Vaccination dramatically reduced this burden, but the group most affected remains children under five years old, particularly infants who are just starting and completing the vaccine series. Older children, teenagers, and adults have much lower incidence due to prior immunity from vaccination and the maturation of the immune system. So the best answer is children under five. While newborns can be affected, the overall highest burden sits with those under five.