Smallpox

Prophylaxis

Vaccine: Smallpox vaccine (vaccinia virus) is most often administered by intradermal inoculation with a bifurcated needle, a process that became known as scarification because of the permanent scar that resulted. The current smallpox vaccine is the Wyeth DryvaxTM, which is a licensed product derived from calf lymph; future smallpox vaccines will be grown on human cell cultures. Primary vaccinees receive three punctures with the needle, repeat vaccinees receive 15. Vaccination after exposure to weaponized smallpox or a case of smallpox may prevent or ameliorate disease if given as soon as possible and preferably within 7 days after exposure. A vesicle typically appears at the vaccination site 5-7 days after inoculation, with associated erythema and induration. The lesion forms a scab and gradually heals over the next 1-2 weeks; the evolution of the lesion may be more rapid, with less severe symptoms, in those with previous immunity.

Side effects include low-grade fever and axillary lymphadenopathy. The attendant erythema and induration of the vaccination vesicle is frequently misdiagnosed as bacterial superinfection. More severe vaccine reactions (more common in primary vaccinees) include inadvertent inoculation of the virus to other sites such as the face, eyelid, or other persons (~ 6/10,000 vaccinees), and generalized vaccinia, which is a systemic spread of the virus to produce mucocutaneous lesions away from the primary vaccination site (~3/10,000 vaccinees). Approximately 1/10000 primary vaccinees will experience a transient, acute myopericarditis. Rare, but often fatal adverse reactions include eczema vaccinatum (generalized cutaneous spread of vaccinia in patients with eczema), progressive vaccinia (systemic spread of vaccinia in immunocompromised individuals), and post-vaccinia encephalitis.

Vaccination is contraindicated in the following conditions: immunosuppression, HIV infection, history or evidence of eczema, other active severe skin disorders, during pregnancy, or current household, sexual, or other close physical contact with person(s) possessing one of these conditions. In addition, vaccination should not be performed in breastfeeding mothers, in individuals with serious cardiovascular disease or with three risk factors for cardiovascular disease, or individuals who are using topical steroid eye medications or who have had recent eye surgery. Despite these caveats, most authorities state that, with the exception of significant impairment of systemic immunity, there are no absolute contraindications to postexposure vaccination of a person who experiences bona fide exposure to variola. However, concomitant vaccine immune globulin administration is recommended for pregnant and eczematous persons in such circumstances.

Passive Immunoprophylaxis: Vaccinia immune globulin (VIG) is indicated for treating some complications to the smallpox (vaccinia) vaccine (generalized vaccinia with systemic illness, ocular vaccinia without keratitis, eczema vaccinatum, and progressive vaccinia), and should be available when administering vaccine. It is available as an IND through both DoD and the CDC in both intramuscular and intravenous formulations. A formulation of VIG-IV has been licensed, but is currently in very limited supply. The dose for prophylaxis or treatment is 100 mg/kg for the intravenous formulation (first line). If VIG-IV is not available, cidofovir may be of use for treating vaccinia adverse events (second line). The intramuscular VIG formulation (VIG-IM) is dosed 0.6 ml/kg IM (third line). Due to the large volume of the intramuscular formulation (42 ml in a 70-Kg person), the dose would be given in multiple sites over 24-36 hours. Because of decreased potency of existing lots of VIG-IM, DoD does not currently have an active IND application for it. Limited data suggest that VIG may also be of value in postexposure prophylaxis of smallpox when given within the first week after exposure, and concurrently with vaccination. Vaccination alone is recommended for those without contraindications to the vaccine. If greater than 1 week has elapsed after exposure, administration of both products (vaccine and VIG), if available, is reasonable.

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