Reactions to small pox vaccine in naïve and previously-vaccinated individuals.

Two hundred health care workers in England and Wales were vaccinated with the Lister/Elstree strain of the vaccinia virus, and completed health diaries for 21 days or until the lesion had scabbed over. Pain and temperature were measured daily, and all other symptoms recorded freehand by the vaccinee. One hundred and forty two (71%) vaccinees reported pain, of which 25% considered it to be moderate or severe; 32 vaccinees (16%) recorded a temperature of >37.7 degrees C, two of which exceeded 39 degrees C. Other, mainly trivial, adverse events were common; itch was reported in 72%, erythema in 27%, axillary pain or lymphadenopathy in 38%, malaise or flu-like symptoms in 40% and headache in 23%. The incidences of minor adverse events were lower in re-vaccinees, compared with naïve vaccine recipients, significantly so in the case of erythema and general malaise (p=0.001 and 0.006, respectively), perhaps reflecting pre-existing immunity. Major adverse events occurred in two vaccinees (hospital admission, one with cellulitis and one with headache and possible encephalitis), and a further five were treated with antibiotics for local cellulitis. This is the first study to report results derived from active follow-up by diaries in recipients of the Lister/Elstree strain of vaccinia, and to document reductions in trivial adverse events in re-vaccinees.