Benign hypersensitivity reactions to smallpox vaccine.

Area of Science:

• Dermatology
• Vaccinology
• Immunology

Background:

• Smallpox vaccinations have been reinstituted, leading to a resurgence of observed adverse events.
• Adverse cutaneous reactions to smallpox vaccines are being encountered more frequently.
• A distinct reaction pattern, previously uncharacterized, has been identified.

Purpose of the Study:

• To characterize distinct hypersensitivity reaction patterns following smallpox vaccination.
• To report the incidence and clinical features of these reactions in a military population.

Main Methods:

• Patients with adverse cutaneous reactions post-smallpox vaccination were referred to a dermatology clinic.
• Evaluations included skin biopsy, clinical photography, and laboratory testing (direct fluorescent antibody, cultures, PCR) for intact vesicles or pustules.
• Data were collected from a large military population at Fort Hood, Texas.

Main Results:

• Three distinct hypersensitivity patterns were observed: exanthematous, erythema multiforme-like (EM-like), and urticarial.
• These patterns exhibited unique clinical and histopathologic findings.
• Out of 11,058 vaccinees, six showed exanthematous, two urticarial, and one EM-like reaction patterns.

Conclusions:

• A new exanthematous hypersensitivity reaction to smallpox vaccine is described.
• The incidence of hypersensitivity reactions is higher than previously reported.
• Observed reactions were predominantly benign with mild systemic symptoms, occurring more commonly than severe reactions.