Haemophilus influenzae type b, or Hib for short, is a bacteria that can cause as meningitis, bacteremia (infection of the blood), pneumonia, and other serious infections. It has become very rare in Canada and other countries which use the Hib vaccine. The Hib vaccine is part of the combined vaccine recommended for all infants and given at 2, 4, and 6 months of age, with a booster at 18 months of age. The vaccine is very effective in preventing Hib disease. However, it is not 100% effective.
Hib infects only humans. It lives in the back of the nose and throat. People who are immune to Hib can still carry the bacteria in the nose and throat and can spread the bacteria to others. The Hib bacteria is spread by close contact through coughing, sneezing, talking, kissing – by any activity that spreads droplets of secretions from the nose or throat. It is not possible to know exactly how your daughter was exposed to Hib, but someone in close contact with her was a carrier of Hib. There is no way for a person to know they have Hib in their nose or throat because it does not make you sick if you have protective antibodies.
Most babies are born with protective antibodies which they get during the last trimester of pregnancy. The antibodies are transported across the placenta from the mother to the baby. Most mothers have antibody to Hib which is why most babies are protected for a few months after birth. If a mother does not have any antibodies or if a baby is born prematurely (before 32 weeks of pregnancy) then the baby will not have any antibodies either and will be at risk of Hib infection if exposed to the bacteria.