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Smallpox vaccination of Regional Response Groups
WHO guidelines for assessing reaction following smallpox vaccination
Primary vaccination reaction
Three days after vaccination the inoculated site becomes reddened and pruritic. It becomes papular on day 4 and vesicular on day 5 or 6. A red areola surrounds the vesicle, which becomes umbilicated and then pustular by days 8 to 11. At this time the red areola has enlarged tremendously. The pustule begins to dry, the redness subsides, and the lesion becomes crusted between the second and third week. By the end of the third week the scab falls off leaving a permanent scar. At the end of the first week between the vesicular and pustular phases, there may be a variable amount of fever, malaise and regional lymphadenitis.
Re-vaccination reaction
There are two types of re-vaccination response defined by the WHO Expert Committee on Smallpox:
1. Major reaction
A vesicular or pustular lesion or an area of definite palpable induration or congestion surrounding a central lesion, which may be a crust or an ulcer. This reaction indicates that virus multiplication has taken place and that re-vaccination is successful.
2. Equivocal reaction
All reactions other than 'major reactions'. They may be consequences of immunity adequate to suppress virus multiplication, or they may represent only allergic reactions to inactive vaccine. In these cases vaccination technique should be reviewed and a decision on further re-vaccination made.
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