Our bodies are vulnerable to infections from many bacteria and viruses. Because of that we have many natural defenses, collectively called the "immune system", designed to fight infections. It is possible to induce immunity with a vaccine made from components of the infecting bug or the toxin (biochemical poisons) that some bacteria produce, which will prevent future infections with the natural, full-strength bug.

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.

Vaccines work most of the time, but not always. Most childhood vaccinations work between 90% and 100% of the time. Sometimes, though, a child may not respond to certain vaccines, for reasons that aren’t entirely understood. They are very safe. But like any medicine, they are not perfect. They can cause reactions. Usually these are mild, like a sore arm or slightfever. Serious reactions are very uncommon.

Q.   Are vaccines safe?

A.   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.

Q.   Do vaccines provide better immunity than natural infections?

A.   Vaccines interact with the immune system to produce an immune response similar to that produced by the natural infection, but they do not cause the disease or put the immunized person at risk of its potential complications.