Professional Reference articles are designed for health professionals to use. They are written by UK doctors and based on research evidence, UK and European Guidelines. You may find one of our health articles more useful.
See also separate article Smallpox.
Introduction and history
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 immunisation 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 and 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. There is now no indication for routine smallpox vaccination.
Smallpox is caused by the variola virus, a DNA virus, with 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.
Adverse effects of vaccination
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 generalised vaccinia (241/million vaccinations).
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 the age of 1 year.
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.
Laboratory workers should be informed of the need for vaccination when appropriate. They may have fears about adverse effects which need to be addressed. Concerns have been expressed about smallpox in relation to bioterrorism and the availability of vaccine when half of the world's population is unvaccinated. Vaccines for the protection of troops need to be maintained.
Further information and advice
- If wider use of vaccine is being considered, see "Guidelines for smallpox response and management in the post-eradication era".
- 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 contra-indications from the Public Health Laboratory Service (PHLS) Virus Reference Division; Tel: (+44) 020 8200 4400.
- Advice on laboratory diagnosis can be obtained from the Health Protection Agency (HPA) Viral Zoonosis Reference Unit, Enteric and Respiratory Virus Laboratory, 61 Colindale Avenue, London, NW9 5HT Tel: 0208 200 4400 Email: firstname.lastname@example.org. Out of hours contact details are held by the 24-hour Communicable Disease Surveillance Centre (CDSC) on-call duty doctor; Tel: (+44) 020 8200 6868.
- Advice on clinical diagnosis and treatment can be obtained from Regional Infectious Disease Units, and also from Royal Free Hospital Infection Services, 10th Floor, Royal Free Hospital, Hampstead, London, NW3 2QG; Tel: (+44) 0207 830 2606 Email: email@example.com. Out of hours contact details are held by the 24-hour CDSC on-call duty doctor; Tel: (+44) 020 8200 6868.
- Advice on public health is held by the 24-hour CDSC on-call duty doctor; Tel: (+44) 020 8200 6868.
When required, vaccine can be obtained from:
- Public Health Laboratory Service (PHLS); Tel: (+44) 020 8200 4400
Further reading and references
Riedel S; Edward Jenner and the history of smallpox and vaccination. Proc (Bayl Univ Med Cent). 2005 Jan18(1):21-5.
Belongia EA, Naleway AL; Smallpox vaccine: the good, the bad, and the ugly. Clin Med Res. 2003 Apr1(2):87-92.
Benzekri N, Goldman E, Lewis F, et al; Laboratory worker knowledge, attitudes and practices towards smallpox vaccine. Occup Med (Lond). 2009 Oct 28.
Arita I; Smallpox vaccine and its stockpile in 2005. Lancet Infect Dis. 2005 Oct5(10):647-52.
Artenstein AW; Vaccines for military use. Vaccine. 2009 Nov 527 Suppl 4:D16-22.
Department of Health; Guidelines for smallpox response and management in the post-eradication era (smallpox plan).