This news story requires a bit of background: First, a number of groups of people cannot be given the smallpox vaccine because they have compromised immune systems; these include patients with AIDS and patients undergoing chemotherapy. In addition, patients with eczema cannot have the vaccine; a 2007 article in Science recounted the case of a two-year-old boy with eczema who acquired exzema vaccinatum, a potentially fatal disease, from his recently-vaccinated father (a member of the military). Eczema vaccinatum, although unusual today because so few people receive the vaccine, was a side effect often seen in children through the 1960s. Today, researchers are trying to design vaccines that are safer for these vulnerable populations. To do so, they must understand the exact mechanism by which immuno-compromised people and eczema sufferers react to vaccinia (http://www.sciencemag.org/cgi/content/full/316/5830/1418).
A study published today by researchers at La Jolla Institute for Allergy & Immunology identifies what appears the underlying cause of the severe reaction of people with eczema to the smallpox vaccine. The research was conducted in mouse models with eczema by a husband/wife research team, Toshiaki and Yuko Kawakami. The researchers administered the smallpox vaccine to mice with eczema and found that IL-17 cell levels were higher in mice who developed eczema vaccinatum than in normal mice. IL-17 cells inhibit Natural Killer cell (NK) activity; NKs are cells of the immune system that fight disease. Because of this inhibition, NKs were slower in responding to vaccinia in mice who developed eczema vaccinatum than in normal mice. The researchers tested this theory by stimulating increased NK cell activity in mice with eczema, and they found that the higher activity eliminated eczema vaccinatum.
Eczema, the common name for atopic dermatitis, affects 17% of children in the US. Eczema vaccinatum has a fatality rate of 5-10%, so these children, as well as the people they live with, cannot receive the smallpox vaccine. They are vulnerable should smallpox ever reemerge in the world by accident or through biological warfare. The new knowledge from this study may allow researchers to develop therapies to boost the NK cells in eczema patients, thus allowing these patients to receive the smallpox vaccine.
This article shows that smallpox vaccine research continues today, and that one of the principal aims of the research program is to discover why some people react poorly to vaccinia. That information may then be used to design safer vaccines to protect the population from bio-terrorism. Research on smallpox such as this is one argument for keeping smallpox stocks available - without this kind of knowledge, we would not be able to protect certain groups of people in the event that mass vaccination was needed. This new knowledge has the potential to save lives in the future. Weighing that benefit with the risks of retaining the stores of smallpox, however, becomes extremely tricky.
The journal article is "Inhibition of NK cell activity by IL-17 allows vaccinia virus to induce severe skin lesions in a mouse model of eczema vaccinatum" in the Journal of Experimental Medicine.
The ScienceDaily article can be found at: http://www.sciencedaily.com/releases/2009/05/090525105433.htm