badgerjeans

vaccines don't always work on people with immune system deficiency/ on immuno-suppressants, like people after surgeries, transplants, or who have hiv, lupus etc as well as babies who haven't developed immune systems yet or those with weakened immune systems due to age/alcohol abuse/disease etc

most vaccines are 60-99% effective even if you're healthy and have been vaccinated you can still get sick if the disease is heavily present.