Haemophilus influenzae is a type of bacteria that can cause various infections, particularly in young children and individuals with weakened immune systems. It is known for causing illnesses such as pneumonia, meningitis, and ear infections. There are different strains of this bacterium, with some being more harmful than others. Vaccination has significantly reduced the incidence of severe diseases caused by Haemophilus influenzae type b (Hib), which was once a leading cause of bacterial meningitis in children. The Hib vaccine is now part of routine childhood immunizations, helping to protect against these serious infections.