At what age are pure polysaccharide vaccines typically not recommended due to an immature immune system?

Pure polysaccharide vaccines are designed to elicit a T-cell independent immune response, which is not fully functional in young children. Specifically, the immune system of children under the age of 2 years is still developing, resulting in an inadequate and ineffective response to these types of vaccines. The immaturity of their immune systems leads to a higher likelihood of not achieving protective immunity when such vaccines are administered at this age.

As children grow older, their immune systems mature, and by the age of 2 years, they are generally considered able to mount a more adequate response to polysaccharide vaccines. Consequently, vaccination strategies are often adjusted to accommodate this development, recommending that pure polysaccharide vaccines be reserved for children who are at least 2 years old. This strategic timing helps ensure the effectiveness of the vaccination and enhances the child's ability to develop long-term immunity.