Transmission of vaccinia virus and rationale for measures for prevention.

Currently, health care workers (HCWs) in the United States are being vaccinated against smallpox, and there is a possibility that this will be expanded to a more widespread vaccination program. Inadvertent transmission of vaccinia virus to patients with illnesses that are contraindications to vaccination is theoretically possible. Vaccinia virus is shed from the vaccination lesion of healthy primary vaccinees from approximately the third day to the end of the third week after vaccination; transmission of vaccinia virus is rare but does occur. Prudent management of the vaccination site by HCWs should virtually eliminate transmission. We recommend that vaccinated HCWs cover the site with loose gauze dressings and, when caring for patients with immunosuppression or extensive disruptive skin disorders, cover the dressings with semipermeable membranes. The evidence for respiratory spread of vaccinia virus is not compelling, and therefore droplet or airborne infection precautions should not be necessary, even for vaccinated HCWs who are caring for patients who experienced serious adverse events after smallpox vaccination in the past.