We can vaccinate against any disease

Vaccines are the best defence against contagious diseases, but there are still many, against which we cannot vaccinate. One example is HIV. Scientists have tried to develop an HIV vaccine for years. The lack of success is due to the fact that the virus is different from the infections against which we normally vaccinate. HIV mutates extremely fast, weakening the very immune system that a vaccine is to activate. A more basic problem is that scientists normally identify the substances that make the immune system react by studying people who have developed natural immunity by combating the disease, but HIV does not leave many survivors. Some bacteria and viruses can cause cancer, such as HPV, which can cause cervical cancer; and Hepatitis C, which can cause liver cancer. There is a vaccine against HPV, but no vaccine against Hepatitis C. Now, DNA technology has introduced alternatives, and in the future, we will probably develop vaccines against both HIV and several types of cancer.