Scottish Government

Interim Guidelines for Smallpox Response and Management in Scotland in the Post-Eradication era

II Introduction

1. Smallpox (variola) was one of the most severe infectious diseases affecting humans. It was present throughout the world during most of recorded history. It is specifically a human disease with no reservoir in any animal species. The infection no longer exists in nature, having been declared eradicated in 1980 following a global campaign led by the WHO.

2. Smallpox virus is a DNA virus. It is a member of the genus orthopox virus, which includes vaccinia and monkeypox. Only smallpox is readily transmissible from person to person.

3. The last community-acquired case was in Somalia in 1977. Following eradication in 1980 the WHO recommended that all countries cease vaccination. Routine vaccination in the UK and other European countries had ceased prior to this in the 1970s. Knowledge of the natural history of smallpox is from historical records and the personal experience of a relatively small number of senior physicians, microbiologists and epidemiologists who dealt with the disease in the past.

4. Patients are infectious with the onset of fever (see Section IV), however the typical vesicular rash (see Section III) does not appear until 4 to 7 days later. The rash is preceded by a prodromal period of 1 to 3 days of fever, malaise, headache and backache followed by 2 to 4 days of a macular rash. Clinical pictures to illustrate the rash can be found on the PHLS website: http://www.phls.org.uk/topics_az/smallpox/pictures.htm

5. Control and ultimately eradication of smallpox was achieved by vaccination. The vaccine is based on vaccinia virus, a live virus of low pathogenicity. Although effective in the eradication of smallpox, the vaccine can cause serious adverse effects, and for this reason vaccination in the UK was discontinued in the 1970s because the risks from vaccination outweighed the risks from disease. In the absence of any clear evidence that smallpox may re-emerge, this remains the case. In the event of an outbreak, the containment strategy will centre on isolation of cases and vaccination of contacts. However, it is planned that sufficient supplies will be available to vaccinate the entire population of Scotland and the rest of the UK should this be deemed necessary.

6. The duration of complete immunity provided by vaccination is uncertain, but is unlikely to be more than 10 years. Previously vaccinated individuals are therefore unlikely to be protected from infection although the disease may be less severe. They will develop immunity more quickly on revaccination.