Secondary and Tertiary Transfer of Vaccinia Virus Among U.S. Military Personnel --- United States and Worldwide, 2002--2004

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In December 2002, the Department of Defense (DoD) began vaccinating military personnel as part of the pre-event vaccination program (1). Because vaccinia virus is present on the skin at the site of vaccination, it can spread to other parts of the body (i.e., autoinoculation) or to contacts of vaccinees (i.e., contact transfer). To prevent autoinoculation and contact transfer, DoD gave vaccinees printed information that focused on hand washing, covering the vaccination site, and limiting contact with infants (1,2). This report describes cases of contact transfer of vaccinia virus among vaccinated military personnel since December 2002; findings indicate that contact transfer of vaccinia virus is rare. Continued efforts are needed to educate vaccinees about the importance of proper vaccination-site care in preventing contact transmission, especially in household settings.

DoD conducts surveillance for vaccine-associated adverse events by using automated immunization registries, military communication channels, and the Vaccine Adverse Events Reporting System (VAERS). Contact transfer cases are defined as those in which vaccinia virus is confirmed by viral culture or polymerase chain reaction (PCR) assays. Other cases are classified as suspected on the basis of lesion description and reported linkage to a vaccinated person 3--9 days before lesion development.

During December 2002--January 2004, a total of 578,286 military personnel were vaccinated; 508,546 (88%) were male, and 407,923 (71%) were primary vaccinees (i.e., received smallpox vaccination for the first time). The median age of vaccinees was 29 years (range: 17--76 years). Among vaccinees, cases of suspected contact transfer of vaccinia were identified among 30 persons: 12 spouses, eight adult intimate contacts, eight adult friends, and two children in the same household. These cases were reported from Colorado (four), North Carolina (four), Texas (four), Alaska (two), California (two), Connecticut (one), Kansas (one), New Jersey (one), Ohio (one), South Carolina (one), Washington state (one), West Virginia (one), and overseas (seven). The sources of suspected contact transfer were all male service members who were primary vaccinees. Except for six male sports partners, all infected contacts were female.

Vaccinia virus was confirmed in 18 (60%) of the 30 cases by viral culture or PCR. Sixteen (89%) of the 18 confirmed cases involved uncomplicated infections of the skin; two (11%) involved the eye (3). None resulted in eczema vaccinatum or progressive vaccinia. Twelve (67%) of the 18 confirmed cases were among spouses or adult intimate contacts. The observed rate of contact transfer was 5.2 per 100,000 vaccinees overall or 7.4 per 100,000 primary vaccinees. Among 27,700 smallpox-vaccinated DoD health-care workers, no transmission of vaccinia from a vaccinated health-care worker to an unvaccinated patient or from a vaccinated patient to an unvaccinated health-care worker has been identified.

Two (11%) of the 18 confirmed cases of transfer of vaccinia virus resulted from tertiary transfer. One involved a service member, his wife, and their breastfed infant; the other involved serial transmission among male sports partners.

Case Reports

Case 1. In early May 2003, a service member received his primary smallpox vaccination. Approximately 6--8 days after vaccination, he experienced a major reaction (i.e., an event that indicates a successful take; is characterized by a papule, vesicle, ulcer, or crusted lesion, surrounded by an area of induration; and usually results in a scar) (4). The vaccinee reported no substantial pruritus. He slept in the same bed as his wife and kept the vaccination site covered with bandages. After bathing, he reportedly dried the vaccination site with tissue, which he discarded into a trash receptacle. He also used separate towels to dry himself, rolled them so the area that dried his arm was inside, and placed them in a laundry container. His wife handled bed linen, soiled clothing, and towels; she reported that she did not see any obvious drainage on clothing or linen and had no direct contact with the vaccination site.

In mid-May, the wife had vesicular skin lesions on each breast near the areola but continued to breastfeed. Approximately 2 weeks later, she was examined at a local hospital, treated for mastitis, and continued to breastfeed. The same day, the infant had a vesicular lesion on the upper lip, followed by another lesion on the left cheek (5). Three days later, the infant was examined by a pediatrician, when another lesion was noted on her tongue. Because of possible early atopic dermatitis lesions on the infant's cheeks, contact vaccinia infection with increased risk for eczema vaccinatum was considered. The infant was transferred to a military referral medical center for further evaluation. On examination, the infant had seborrheic dermatitis and no ocular involvement. Skin lesion specimens from the mother and infant tested positive for vaccinia by viral culture and PCR at the Alaska Health Department Laboratory and at Madigan Army Medical Center. Because both patients were stable clinically and the lesions were healing without risk for more serious complications, vaccinia immune globulin was not administered. Neither patient had systemic complications from the infection.

Case 2. In July 2003, a service member who had been vaccinated was wrestling with an unvaccinated service member at a military recreational function when the bandages covering the vaccination site fell off. The unvaccinated service member subsequently wrestled with another unvaccinated service member. Six days later, both unvaccinated service members had lesions on their forearms, neck, and face. Skin lesion specimens from both men tested positive for vaccinia virus by PCR and viral culture at Tripler Army Medical Center's microbiology laboratory.

Reported by: TW Barkdoll, MD, Okinawa, Japan. RB Cabiad, Fort Richardson; MS Tankersley, MD, JL Adkins, MD, Elmendorf Air Force Base; B Jilly, PhD, G Herriford, Alaska Public Health Laboratory. AC Whelen, PhD, CA Bell, PhD, Tripler Army Medical Center, Honolulu, Hawaii. MP Fairchok, MD, LC Raynor, MD, VA Garde, MD, VM Rothmeyer, SD Mahlen, PhD, Madigan Army Medical Center, Fort Lewis, Washington. RJ Engler, MD, LC Collins, MD, LL Duran, Vaccine Healthcare Center Network, Walter Reed Army Medical Center; MT Huynh, MD, RD Bradshaw, MD, Bolling Air Force Base, Washington, DC. JD Grabenstein, PhD, Military Vaccine Agency, U.S. Dept of Defense.

Editorial Note:

The findings in this report indicate that the primary risk for secondary transfer of vaccinia was among persons who shared a bed; 12 of the 18 confirmed cases were spouses or adult intimate contacts. However, the majority of vaccinated DoD personnel who shared a bed did not transfer vaccinia virus to their contacts. The frequency of contact transfer in the military vaccination program is comparable to rates observed during the 1960s, although persons are less likely to be immune to vaccinia today and thus are more susceptible to contact transfer (1).

The first case of tertiary transfer described in this report underscores the need for breastfeeding mothers with household contact with vaccinees to take precautions to prevent inadvertent transmission of vaccinia to their infants. Direct contact is presumed to be the major mode of transmission, but clothing and bed linen might act as vectors for secondary transmission. Tertiary transmission, although rare, is facilitated when the secondary infection is not recognized.

Programs that educate health-care workers, vaccinees, and contacts should note that new vesicles or pustules that appear <15 days after the vaccinia scab falls off from the vaccination site might be vaccinia infections. Although an infant living in the home is not a contraindication to vaccination of a family member in a nonoutbreak setting, measures to prevent transmission include having vaccinees launder their own linens and towels and change their bandages away from other household members.

During the 1960s, the rate of unintentional infection with vaccinia in secondary contacts was two to six cases per 100,000 primary vaccinees (4,6,7). During that period, two thirds of reported contact infections occurred among children, typically siblings. Such spread could manifest as an inadvertent infection or, in more severe fashion, as eczema vaccinatum or progressive vaccinia. Infections of the skin predominated, with rarer ocular involvement posing a risk for scarring or keratitis. In the current DoD smallpox vaccination program, no cases of eczema vaccinatum have occurred, although the population of atopic dermatitis patients might have increased substantially since the 1960s (8). During the 1960s, eczema vaccinatum resulted in deaths, and two thirds of such cases were related to contact transfer of vaccinia virus (6). In the current DoD smallpox vaccination program, careful screening of DoD vaccinees and their household contacts for skin diseases along with targeted education likely contributed to both screening out vaccine candidates with personal or close-contact contraindications and educating vaccinees about proper infection-control measures.

Health-care workers and the public should report suspected cases of contact transfer of vaccinia virus to their state or local health departments and to VAERS at http://www.vaers.org, or by telephone 800-822-7967. Viral culture or PCR assays, important for confirming vaccinia virus, are available from the majority of state public health laboratories.

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