Smallpox: What the Dermatologist Should Know

Phyllis I. Spuls, MD; Jan D. Bos, MD, PhD; Donald Rudikoff, MD

Disclosures

Skinmed. 2004;3(4) 

In This Article

Vaccination

Both pre-exposure and postexposure vaccination strategies have been developed by public health officials in the event of a bioterrorist attack. It is thought that one or two deaths per million vaccinees would occur in any mass vaccination program. Moreover, various severe side effects result from vaccination, and these would be more likely than in the past because so many individuals are now immunosuppressed, such as those with human immunodeficiency virus infection, patients on chemotherapy, and organ transplant recipients. Risks and benefits of preemptive widespread or limited vaccination must be weighed against the very small chance of smallpox attack. Most of the controversy has centered on whether the ring vaccination technique used in the global smallpox eradication campaign would be effective in a bioweapons attack. Conflicting mathematical models and scenarios have been published.

According to one "pre-attack" plan, up to 10 million health and emergency workers should routinely be vaccinated. Others have proposed vaccination on demand. Advocates of mass vaccination point out that if even half the population were vaccinated in advance, everyone would be safer because fewer people would be capable of spreading the infection (herd immunity effect).

Postattack vaccination proposals include ring vaccination and/or widespread vaccination of the entire population or of individuals demanding vaccination. Ring vaccination was effectively used for natural outbreaks and was the strategy used for eradication of natural smallpox. The protocol involves isolating anyone with a suspected case of variola and quickly vaccinating that person's primary contacts (friends, family, and coworkers) and secondary contacts (contacts of the contacts) in an expanding circle. Some think this strategy would be insufficient for large, multifocal bioterrorist attacks[33] or that it would be more effective if mass vaccination as also used to increase herd immunity in the population.[34] One mass vaccination plan suggests that 3000 people could be vaccinated in an 8-hour shift.[35]

Despite earlier concerns about unavailability of adequate smallpox vaccine stores, it now appears that the United States will soon have enough vaccine to vaccinate the entire population. Studies have investigated whether dilution of existing smallpox vaccine decreases its effectiveness. The current vaccinia virus vaccine (Dryvax; Wyeth Laboratories, Marietta, PA) can be diluted to a titer as low as 1:10 (107.0 pfu/mL [approximately 10,000 pfu/dose]) and still induce local viral replication and vesicle formation in more than 97% of persons.[36] A second-generation vaccine grown in cell cultures is now available.

Previously, primary vaccination was performed using a bifurcated needle and five needle sticks for primary vaccinees and 15 sticks for revaccination. Current recommendations are that 15 needle sticks be used for all vaccinees. The technique, dermal scarification, induces a localized productive infection that triggers a vigorous immune response. Antibodies induced against vaccinia are cross-reactive and protective against smallpox and remain in the body for years afterward. However, immunity may wane after several years. The exact correlation between antibody titer and level of immunity to smallpox has never been demonstrated.[37] Periodic revaccination was necessary to guarantee adequate immunity.

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