Vaccines are considered by many people to be a mixed blessing. On the one hand, they are intended to help people to fight a particular microorganism. They can provide the person with a form of immunity to the bad effects of something in their environment that can cause them significant harm or even death. On the other hand, many people worry about whether the vaccines themselves are safe or whether they might have side effects that are worse than the disease that they are aimed at helping to prevent.
Many people would consider vaccines to be one of the most important advances in medicine. The underlying technique is to introduce a particular microorganism into a person in a controlled and understood way rather than letting them catch it in the wild. The point of this is to provide the immune system with examples upon which antibodies can be built that can identify such entities in the future and lead to their destruction and the prevention of some potentially nasty and even fatal disease.
One such technique involves the use of small amounts of live versions of the microorganism in question. But another possibility is the use of an attenuated version of the entity. In this case, much of the structural information will be retained for use by the immune system but with some key aspect of the entity deactivated. A third possible approach involves the use of killed microorganisms. Again, useful structural information is preserved but without the entity being dangerous.
Of course, all of this talk of introducing a potentially harmful microorganism into a healthy individual strikes fear into some people. Often they worry about catching the disease, or about it not working, or about it having worse side effects than the disease itself. Perhaps even being fatal. Realistically, though, vaccines have saved vastly more lives than they have taken. Despite this, public opinion, in some cases fueled by media frenzies and panic-spreading, has brought some vaccinations such as the measles, mumps, and rubella (MMR) jab under question without any evidence.
There are even some people who object to vaccination programs for reasons that have nothing to do with the effectiveness or potential side effects of the vaccine, but have rather to do with spurious religious or moral arguments. On balance, though, the use of vaccines should certainly continue but testing of the vaccines before use should be rigorous, and public information about the disease, the vaccine, and the testing process should be clear and made easily available.