Which vaccine was the first to prevent a bacterial infection that causes severe diarrhea and pneumonia in children?

Pneumococcal conjugate vaccines were developed to protect against Streptococcus pneumoniae, a bacterium that can cause pneumonia, meningitis, blood infections, and ear infections. These vaccines became an important part of childhood immunization in the early 2000s, replacing older polysaccharide approaches for young children. Because they cover multiple serotypes, they sharply reduced invasive pneumococcal disease in many countries. They are among the most important vaccines for preventing severe bacterial illness in childhood.