The World Health Organization (WHO) recommends that the site of smallpox vaccination be examined 6-8 days after the vaccine has been administered. Development of a major reaction at the site indicates that full protection immunity has been achieved. Failure to develop a major reaction may indicate that the patient may have inadequate protection.

Major reactions indicative of immunity:

(1) response after primary vaccination

(2) response after revaccination


Major reaction indicative of immunity – after primary vaccination:

(1) At 3-4 days after the vaccination the lesion is red and pruritic.

(2) A vesicle develops with a surrounding red areola.

(3) The lesion then becomes umbilicated and then pustular by 7-11 days after vaccination.

(4) The lesion then becomes crusted and regresses over the next 7-14 weeks.

(5) After the scab falls away there is an area of permanent scarring,


Major reaction indicative of immunity – after revaccination:

(1) This may be less pronounced, evolve faster and or heal faster than after a first time vaccination.

(2) A reaction is positive if at 6-8 days after vaccination one of the following lesions is seen

(2a) a pustular lesion

(2b) an area of induration

(2c) area of congestion about a central scab or ulcer


Failure to develop an adequate reaction:

(1) immune response sufficient to suppress viral multiplication

(2) impotent vaccine

(3) poor vaccination technique

(4) allergic reaction


If an inadequate reaction is observed, then a repeat vaccination is performed by a competent person using vaccine from a fresh vial from a different lot.


If the repeat vaccination fails to elicit a major reaction, then the health care provider should contact the local or state health department or the CDC for advice.

To read more or access our algorithms and calculators, please log in or register.