Currently, there are two types of vaccines commonly used to prevent pneumococcal diseases. One type is the 23-valent polysaccharide vaccine, suitable for high-risk populations over two years old. The other type includes the 7-valent or 13-valent conjugate vaccines, used for vaccinating infants under two years old. The vaccination schedule for the 7-valent or 13-valent vaccines follows a "three plus one" program, which means three primary immunization doses with at least one month between each dose, followed by a booster dose. For the 23-valent vaccine, high-risk individuals over two years old generally require only a single dose; however, immunocompromised patients may need a booster shot, typically recommended five years after the initial vaccination.