Why is it that some immunized children still get ill from the disease(s) they were immunized against?

There are many possible explanations to this. First, not all causes of a disease may be prevented by vaccination alone. For example, many organisms cause pneumonia and meningitis, but pentavalent and pneumococcal conjugate vaccines protect against the two most common organisms that cause them – Haemophilus infuenza type B (HIB) and Streptococcus pneumoniae. Second, a vaccine that is not stored within the recommended temperature (+2 to +8 degrees Celsius) at the health facility level may lose its potency and become ineffective when administered to clients. In addition to vaccines, good environmental hygiene and regular hand washing with soap and water help to protect children and adults from many infectious diseases.