Since the 1970s, smallpox vaccination has been associated with numerous cutaneous reactions, most of which have been reported with the first-generation Dryvax. Minor local reactions occurred in approximately 2% to 6% of vaccinees in clinical trials.9 These reactions included local edema involving the upper arm, satellite lesions within 2.5 cm of the vaccination site, local lymphadenopathy, intense inflammation or viral cellulitis surrounding the inoculation site, and viral lymphangitis tracking to axillary lymph nodes. In clinical trials, these reactions were self-limited and required only symptomatic treatment.9
Autoinoculation is another cutaneous reaction that can occur because Dryvax and ACAM2000 both contain live-attenuated replicating vaccinia virus. Accidental implantation may occur when the high titers of virus present at the vaccine site are subsequently transferred to other sites, especially abnormal mucosa or skin, resulting in an additional primary inoculation site.10
Eczema vaccinatum is a potentially life-threatening reaction that may occur in patients with disruptive skin disorders, such as atopic dermatitis. These patients are at risk for massive confluent vaccinia infection of the skin.10 In patients with atopic dermatitis, the virus rapidly disseminates due to both skin barrier dysfunction and impaired immunomodulation, resulting in large confluent skin lesions and the potential for viremia, septic shock, and death.10,11 Mortality from eczema vaccinatum may be reduced by administration of vaccinia immune globulin.10
The vaccinia virus also may spread hematogenously in healthy individuals,10 resulting in a benign reaction called generalized vaccinia. These patients develop pustules on areas of the skin other than the vaccination site. Although typically benign and self-limited, Beachkofsky et al4 described a case of generalized vaccinia in a healthy 34-year-old man resulting in a rapidly progressive vesiculopustular eruption with associated fever and pancytopenia. The patient made a complete recovery over the course of the following month.4
Alternatively, progressive vaccinia is a severe complication of smallpox vaccination seen in patients with impaired cell-mediated immunity. It also is known as vaccinia gangrenosum or vaccinia necrosum. These patients develop expanding ulcers due to exaggerated viral replication and cell-to-cell spread of the vaccinia virus.10,11 Hematogenous spread may result in viral implantation at distant sites of the body. This disease slowly progresses over weeks to months, and it often is resistant to treatment and fatal in patients with severe T-cell deficiency.10
Acral papulovesicular eruption is a distinct cutaneous adverse event following smallpox vaccination. Although further research is needed to discern the pathogenesis of this reaction, it is benign and self-limited, and patients have fully recovered with supportive care. In addition, a modified vaccinia Ankara vaccine (Bavarian Nordic) was approved by the US Food and Drug Administration in 2019.12,13 It is a nonreplicating attenuated viral vaccine that had fewer adverse events compared to ACAM2000 in clinical trials.13 To date, papulovesicular eruptions have not been reported following vaccination with the modified vaccinia Ankara vaccine; however, continued monitoring will help to further characterize any cutaneous reactions to this newer vaccine.