The reason for this is that a small number of people who are vaccinated against a particular disease fail to build the immunity to fight off the illness. Some also ‘outgrow’ the vaccine – which is why booster shots are so important! When they are exposed to the illness in question, they can contract it. The risk of being vaccinated and still contracting a disease is around 1% – which is much lower than the risk for unvaccinated people.
Looked at slightly differently, this means that your child has a 1% risk of contracting a disease that he or she has been vaccinated against, as opposed to a 100% risk for an unvaccinated person who comes into contact with that disease. So while vaccines are not one hundred percent fool proof, they definitely increase your odds, and your child’s odds, of avoiding disease.