If a baby can get a disease even after giving the vaccine, then why are vaccines important and how effective they are?
Vaccines are not 100% effective. There is always a slight chance to catch infections even after immunization. But post vaccination, symptoms of the disease are usually much milder and infection normally does not progress to serious disease. Vaccinated person might get sick in cases, where infection occurred just before vaccination, or right after vaccination. A minimum of 2 weeks are required to gain immunity after vaccine is administered.