Which type of vaccine stimulates B cells without the help of T helper cells?

The answer is correct because pure polysaccharide vaccines are unique in their mechanism of action. These vaccines consist of long chains of sugar molecules that make up the surface capsule of certain bacteria. When administered, pure polysaccharide vaccines can activate B cells directly without necessitating the involvement of T helper cells. This allows for a rapid response because B cells can produce antibodies upon recognition of the polysaccharide structure.

In contrast, other types of vaccines, such as live attenuated and inactivated vaccines, generally rely on the presentation of antigens to T helper cells, which then assist in activating B cells. Purified protein vaccines also depend on T helper cells, as they present protein antigens that require help from T cells to generate a strong antibody response. Therefore, the distinct characteristic of pure polysaccharide vaccines to stimulate B cells independently is what makes this option the correct answer.