There are diseases where there are vaccines. In most cases, people who are vaccinated will no longer get the disease. In some cases, people who have been vaccinated will still catch the disease they have been vaccinated against. This is known as breakthrough infection. In some cases, vaccines do not provide immunity against the pathogen. Breakthrough infections have been described for diseases such as mumps, varicella (chicken pox), and influenza. As the person has been vaccinated, the disease will look different, in most cases: Usually, the symptoms will be milder, and it may not last as long (compared to someone who has not been vaccinated, and who naturally contracted the disease).