Approved vaccines are safe because they go through a rigorous system of testing before being introduced. Sometimes vaccines cause mild side effects that will not last long; some people may feel unwell and have a sore arm for 2-3 days. On the balance of evidence on benefits and adverse outcomes, vaccines are given authorization (emergency or full) for use. A monitoring system for adverse events is maintained even after licensure to ensure that any events that could have been missed or whose manifestation take long to happen are captured. Vaccines protect not only the people who receive them from many serious diseases, but also people who cannot have vaccines, by helping to stop disease spreading. If enough people get vaccinated, then vaccines will reduce or even get rid of some diseases.