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Smallpox vaccination of Regional Response Groups

Complications of smallpox vaccination

Local complications and fever

These reach a peak on days 7-13 after vaccination. Local erythema up to 2 cm in diameter occurs in 30-50% of recipients, and 7-10% have larger areas of erythema, sometimes up to 10 cm or more. Axillary lymphadenopathy, often tender or painful, affects 25-30% of recipients.

Satellite lesions

These are reported in about 5% of cases, and are usually local, in the upper arm on the vaccinated side.

Allergic rashes and erythemas

These occur within 5 to 10 days after vaccination and range from non-specific erythhemas to a distinct erythema multiforme syndrome (typical 'target' or 'bullseye' lesions).

Inadvertent self-inoculation or infection of others

Viruses can be transferred from the vaccination lesion to distant skin sites, or to the skin of other individuals, on the unwashed hands or by close contact (during childcare, between sexual partners or during sporting activities). Transfer to other individuals who are immunosuppressed, who have eczema or are otherwise susceptible, can cause severe disease. Transfer to the eye (vaccinia keratitis), or the genital area can also cause severe complications.

Generalised, or disseminated, vaccinia

Typical vaccinia pustules appear on body sites distant from the vaccination site, and follow the same normal evolution as the vaccine pustule. Although the condition appears alarming, it rarely causes severe disease, and probably represents transient viraemic spread of the vaccinia virus.

Eczema vaccinatum

This is a localised or systemic spread of vaccinia virus to areas of skin affected by eczema. It varies widely in severity; most cases, however, resolve without intensive treatment, but some can be severe or progressive.

Progressive vaccinia or vaccinia necrosum

This rare problem affects immunocompromised individuals, particularly those with severely impaired cell-mediated immunity, but can also occur in agammaglobulinaemia. The vaccinia pustule advances inexorably, by local extension, local satellite lesion formation, and eventually with the appearance of distant satellite lesions, which also expand. There is a high fatality rate, and the condition is difficult to treat.

Post-vaccinial encephalitis

Animal studies suggest that the pathogenesis is related to penetration of the vaccinia virus into the central nervous system. The symptoms are typically fever and headache followed by agitation, sleepiness and fits. Very rarely it may prove fatal.

Rates of adverse events

• Vaccine recipients must be carefully selected in order to minimise the risk of complications. The risk of the most serious complications (eczema vaccinatum, progressive vaccinia, post-vaccinial encephalitis) is low, around 1 in 25 000 for primary vaccination, and may be less with appropriate screening-out of contraindicated people

• The safety and reactogenicity data are historical and based on studies from the UK and USA in the 1950s and 1960s when the vaccinia vaccines were in routine use. Table 2 shows the rates of adverse events per million adults vaccinated (CDSC data). Whilst recorded rates are consistently lower for re-vaccination, data do not allow assessment of whether risk increases with increasing time since previous immunisation.

• Serious vaccine complications occur more frequently in individuals with immunosuppression and chronic skin conditions, in particular eczema (or history of eczema). Direct contact for those with these conditions means they are also at risk.

Table 2: Adverse events in vaccinees per million doses (E&W and USA figures),¹²³⁴

Excluding adverse events in contacts of vaccinees

Based on US 10 state survey data only.

1. Dick G Smallpox: A reconsideration of public health policies. Progr. Med. Virol. 1966; 8: 1-29

2. Dick G. Complications of smallpox vaccination in the United Kingdom. I nternational symposium on smallpox vaccine. Bilthoven 1972; Symp. Series immunobial. Standard 1973; 19; 205-215

3. Lane JM et al. Complications of smallpox vaccination 1968. National surveillance in the United States. N. Eng. J. Med. 1969; 281: 1201-1208.

4. Lane JM et al. Complications of smallpox vaccination, 1968: Results of ten statewide surveys. J.Infect. Dis. 1970; 122; 303-309.

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