Smallpox Vaccination

See also or record on Smallpox.

Edward Jenner (1749-1823) published work in 1798 entitled "An enquiry into the causes and effects of the variolae vaccinae". This work was done following earlier observations that dairymaids and cowmen did not catch smallpox although they did catch cowpox. Benjamin Jesty (1737-1816) protected his family in a similar way before Jenner reported the first scientific attempt at immunization from a hut near his home in Berkeley, Gloucestershire. Jenner scratched material from a cowpox pustule into the arm of a young local boy, James Phipps, who subsequently developed a pustule and a fever. He remained healthy when subsequently Jenner inoculated him with smallpox. "Vaccinae" means "of the cow" and "vaccination" means "protection from smallpox". At this time there were 23,000 deaths per year from smallpox in England many more across Europe. The case fatality rate was between 20% and 60%.
In 1853 compulsory smallpox vaccination was introduced and in December 1979 the Global Commission for the certification of Smallpox eradication declared the world free of smallpox. In 1980 this was ratified by the World Health Assembly.¹ There is now no indication for routine smallpox vaccination.

Smallpox is caused by the variola virus, a DNA virus, humans being the only known reservoir for the disease. It is spread by person to person contact with an incubation period of 10 to 14 days. The overall mortality is about 30%.

The most widely used virus used for smallpox inoculation is vaccinia (derived from the genus Orthopoxvirus). This is a double stranded DNA virus sharing antigenicity with the variola virus usually prepared from calf lymph. Research is underway using recombinant DNA techniques to find a safer vaccine without replication of the vaccinia virus. Current vaccines give protection for 5 years (partial immunity for 10 years or more) with 95%conversion rate after primary vaccination and some protection if given within a few days of exposure. It is administered by multiple skin puncture using a bifurcated needle containing small quantities of the vaccine. A papule develops after 3-5 days and becomes vesicular and pustular over 8-10 days followed by scab and scar formation.²

Smallpox vaccine is less safe than other vaccines used routinely today. A third of recipients get mild vaccine related symptoms. More serious reactions occur infrequently: death (1/million vaccinations); eczema vaccinatum (39/million vaccinations); progressive vaccinia (1.5/million vaccinations); post vaccinial encephalitis (12/million vaccinations); and generalized vaccinia (241/million vaccinations).²

Risk factors

Risk factors for complications and adverse effects include eczema, any conditions disrupting the epidermis (acne, psoriasis, burns, seborrhoeic dermatitis etc), the immunocompromised, immunosuppressed patients, pregnancy, and children under 1 year.²

There is no indication for smallpox vaccination except for:

• Workers in laboratories where pox viruses are handled and others whose work involves an identifiable risk of exposure to pox virus.

Concerns have been expressed about smallpox in relation to bio-terrorism and the availability of vaccine when half of the world's population is unvaccinated.³

• If wider use of vaccine being considered see "Guidelines for smallpox response and management in the post-eradication era".⁴
• For further advice and guidance for laboratory staff see Advisory Committee on Dangerous Pathogens and Advisory Committee on Genetic Modification 1990. HMSO ISBN 011885450.
• Advice on the need for vaccination and contraindications from the PHLS Virus Reference Division telephone 020 8200 4400.

When required vaccine can be obtained from:

• PHLS on 020 8200 4400