Questions and answers on immunization and vaccine safety 1. With adequate levels of hygiene, sanitation and clean water, is there still a need for vaccination? Vaccines are necessary — and good hygiene, sanitation, clean water, and nutrition are insufficient for stopping infectious diseases. If we don’t maintain optimum rates of immunization or “herd immunity”, the diseases prevented by vaccination will return. While better hygiene, sanitation and clean water help protect people from infectious diseases, many infections can spread regardless of how clean we are. If people are not vaccinated, diseases that have become uncommon such as pertussis (whooping cough), polio and measles, will quickly reappear. 2. Are vaccines safe? Vaccines are safe. Any licensed vaccine is rigorously tested across multiple phases of trials before it is approved for use, and regularly reassessed once it is on the market. Scientists are also constantly monitoring information from several sourc...