They can conquer smallpox, so why not AIDS?
Indeed, why not the common cold? Smallpox was (hopefully) overcome by vaccines. These are specific substances which are used to trigger the body’s ‘soldier factories’ into making lots of ‘soldiers’ (antibodies) which are designed to kill only a specific, particular type of virus before it can do much damage. (Smallpox, AIDS and the common cold are caused by various types of viruses—AIDS is caused by a virus called HIV, Human Immunodeficiency Virus.)
The reason why vaccines have not succeeded in eliminating influenza, for example, is because the viruses change. Soldiers trained to attack only enemies in grey uniforms will be useless if the enemy changes into blue uniforms. Effective vaccines against particular strains of flu virus constantly need to be updated for this reason.
The same potential problem plagues the development of an effective vaccine against HIV. As the virus multiplies, the ‘copies’ which are made of it often have copying mistakes (mutations) which can change those parts of the virus that your body’s defences are geared to recognize. Only a very small change may be enough—a change which otherwise is completely irrelevant to the structure or function of the virus. So a ‘new strain’ emerges, and although you were able to fight off the first one, now you can’t.
