Professor Emeritus, Pediatrics, University of Arizona Health Sciences Center, Tucson, AZ USA

After a hiatus of more than 30 years, smallpox and smallpox vaccine issues have emerged in the scientific and political landscapes. After the eradication of smallpox in 1977 and the gradual decrease in use of smallpox vaccine in the years thereafter, the only persons who contacted vaccinia virus were those working in laboratories in which the virus was used as a potential vector or as an object of basic science investigation. In this issue of the Journal, Mempel and colleagues report an instance of laboratory acquired vaccinia infection in a worker in just such a laboratory (^{Mempel et al, 2003}). This is not the first instance of a laboratory acquired infection (^{Openshaw et al, 1991}). In addition, one instance of contact vaccinia occurred in an individual from a dog bite while she removed a vaccinia-laden sachet (designed to immunize wild animals against rabies) from his mouth (^{Rupprecht et al, 2001}). These are isolated, rare events in the era between cessation of vaccination and today's revival of activity with vaccinia. We can expect that contact with vaccinia in the laboratory and in the field will increase exponentially as the United States and other countries resume vaccinations and study of the virus in the laboratory.

In the instance reported here, the lab worker examination revealed "Only the palms of both hands showed signs of mild skin barrier disturbance, e.g., small erosions from working with unprotected hands in cold temperature over a prolonged period." In the rabies bait incident the woman infected had epidermolytic hyperkeratosis. One can assume with reasonable assurance that both persons, and others who experience this type of contact vaccinia, had disrupted skin that permitted vaccinia virus to infect (^{Neff et al, 2002}). Patients with atopic dermatitis, Darier's disease, and other disruptive skin diseases are vulnerable to contact inoculation vaccinia. (^{Neff et al, 2002;CDC, n.d.}) In the report published in this issue of the JID, the authors suggest that the immunodulating construct, inserted into vaccinia virus, may have been responsible for the 'take' in the lab worker. That is not necessarily true, as the virus is capable of infecting without assistance from the construct that suppresses adhesion of human peripheral lymphocytes to ICAM-1. The fact that the lesions healed without specific treatment indicates that lymphocytes were active, did get to the site, and did control the virus infection. Had they not done so, one would have expected progressive vaccinia lesions. (^{Fulginiti et al, 1968}).

The lab worker in this instance was not vaccinated, despite guidelines suggesting that all such workers be vaccinated before handling Orthopox viruses (^{CDC, 2001}). Others have argued against vaccination of lab workers (^{Wenzel and Nettleman, 1989}). I believe the rationale raised in the latter letter to Lancet used spurious arguments (i.e., the recombinants are attenuated, the chances for accident are minimal, and if the workers had contact with susceptible patients they might transmit the virus). There will be accidents; I have been consulted on an instance of vaccinia virus splashed onto the face of an experienced lab worker, despite the availability of hoods. The recombinants can produce lesions, as shown in this report, and have been used as efficient vaccinating antigens (^{Cooney et al, 1991}). Safeguards can be provided against spread from vaccination sites (^{CDC, 2002}).

The authors of the current report explain that the recommendations largely originate from the US, and that vaccine is not generally available. Yet, workers at the CDC and at other laboratories have been routinely vaccinated, and given the small number of laboratories worldwide that deal with Orthopox viruses, one would have thought some accommodation could be made to supply each of these labs with vaccine from available stockpiles. If that is not the case, then it should be in the future. The best protection against spread of vaccinia virus in the laboratory is to have a fully immunized staff. Even then, inoculation vaccinia could occur with an injury or disease sufficient to place the virus in direct contact with disrupted skin, although one would expect a more accelerated reaction, given the level of immunity, and no spread from the primary site of inoculation.

In short, all workers with Orthopox viruses should be vaccinated before they contact the virus in the laboratory. Those with dermatologic lesions that might predispose them to contact vaccinia should either refrain from such lab work if possible, or if not, use precautions such as rubber gloves and other protective gear and other measures suggested by the ACIP (^{CDC, 2002}). Useful counselling has been provided by^{Williams and Cooper as well (1993)}.