The first vaccination known to humankind was against a viral infection, when Jenner, in 1796, injected material from a lesion of cowpox into an eight-year-old boy to protect him from smallpox. The culmination of this first step was in 1980 with the declaration that smallpox was the first human infection to be eradicated from the world.

Subsequently, many viral vaccines have been developed and there have been successful public health campaigns to reduce the burden of infection. The World Health Organization (WHO) has an ongoing expanded programme of immunizations (EPI) targeting the worldwide elimination of both polio and measles. Polio is now considered to be non-endemic in all but four countries of the world.

Vaccines against hepatitis B and papilloma viruses can arguably be considered as the first vaccines that protect against cancers (hepatocellular and cervical carcinomas respectively).

Viral vaccines can be divided according to whether they are attenuated or killed.

Attenuated vaccines

Attenuation of virus implies the loss of pathogenicity, but for successful vaccination the immunogenicity has to be maintained. The first example was the smallpox vaccination, which used a related non-pathogenic virus, the cowpox virus.

Attenuation is achieved by selective pressure on the virus during repeated passages in cell culture. The whole process has to be quality controlled strictly to ensure that extraneous viruses have not been introduced and that there is no wild type pathogenic virus in the vaccine.