What is permanent immunity?If you are infected with germs (bacteria or viruses), your immune system usually destroys them. But until then, the germs multiply inside your body and you feel ill as your body fights the infection. If you are infected a second time, your body remembers the invaders and usually destroys them before you start to feel unwell - you are immune. In many cases, doctors can use vaccines to produce this immunity without causing illness.
Why do we need vaccines?
Some bacteria and viruses can make you very ill very quickly. The body does not have enough time to destroy the invaders before it is overwhelmed. Without vaccines, diseases such as diphtheria, polio and smallpox would still kill or disable many people. Worldwide vaccination programs have now wiped out smallpox completely. The only smallpox virus that exists is kept under tight security, deep frozen, in two laboratories in the USA and Russia. Whether or not these stocks should be destroyed is a very controversial subject.