Haemophilus influenzae type b is a polysaccharide-encapsulated bacteria that causes a variety of invasive diseases, such as meningitis, epiglottitis, and pneumonia. Influenza is a virus that causes the disease influenza.
Historical note: Haemophilus influenzae was first isolated in 1889 from the sputum of a patient who died of (viral) influenza disease, and the isolated organism (then called the Pfeiffer bacillus) was incorrectly assumed to have caused the patient’s illness. Haemophilus influenzae received its name in 1920, to acknowledge its historical association with influenza illness. The viral cause of influenza was not discovered until 1933.