Which one of the following best describes the components of vaccines against Haemophilus influenzae disease?

The correct answer is the polysaccharide derived from Haemophilus influenzae conjugated to a protein antigen. This approach is widely used in vaccine development for encapsulated bacteria like Haemophilus influenzae type b (Hib). The polysaccharide component is derived from the bacterial capsule, which is crucial for the bacterium’s virulence. However, polysaccharides alone tend to induce a weak immune response, particularly in young children. Therefore, by conjugating the polysaccharide to a protein carrier, the immune response is significantly enhanced. This conjugation helps stimulate stronger immunological memory and facilitates class switching in B cells, leading to a more robust and long-lasting immunity.

The other methods mentioned, such as using live attenuated or killed strains, or toxoid, do not align with the standard practice for Haemophilus influenzae vaccines. Live attenuated vaccines pose a risk of reverting to a virulent form, and killed vaccines may not effectively stimulate the desired immune response. Toxoids are typically used for bacteria that produce toxins and are not applicable in this case since H. influenzae type b does not produce a significant toxin that warrants this kind of immunization strategy. Hence, the conjugated polysaccharide approach is