Old Smallpox Vaccination Probably Still Protective
Mon August 18, 2003 03:33 PM ET
NEW YORK (Reuters Health) - More than 90% of people who received the smallpox vaccine 25 to 75 years ago show substantial immunity against vaccinia, the virus used in the vaccine, according to a report published in the August 17th online issue of Nature Medicine.
Dr. Mark K. Slifka, from Oregon Health & Science University in Beaverton, and colleagues evaluated the degree and duration of vaccinia immunity after one or more smallpox vaccinations.
Even decades after vaccination, most people showed significant immunity against vaccinia. If these levels of immunity are at least partially protective, then the illness and death rates as a result of an intentional smallpox outbreak would be 'substantially reduced,' the researchers state.
Although this is encouraging news, there are still many individuals born after the mid-1970s who never received the smallpox vaccine. In the event of a bioweapon attack with smallpox, these people would be completely vulnerable to the disease.
Dryvax, the vaccine that eradicated smallpox as a natural disease, was created by growing the viral agent in the skin of calves or other large animals, a production method that is no longer acceptable today. Moreover, there is only enough Dryvax left to vaccinate a few million people, ideally health workers and first responders.
One proposed solution to this vaccine shortage has been to expand the Dryvax stocks through dilution. Unfortunately, even if the effectiveness of the vaccine is not reduced, there would still not be enough vaccine to cover everyone.
Another study in Nature Medicine, however, may provide some good news.
Dr. Richard Weltzin, from Acambis, Inc. in Cambridge, Massachusetts, and colleagues have developed several vaccine candidates derived from the existing Dryvax stocks. Specifically, the researchers were interested in a vaccine that could be manufactured in cell culture in large amounts.
One of the candidates, a clone designated ACAM1000, performed similar to Dryvax in animal studies, so the researchers decided to compare the two in a randomized human study.
In the clinical trial, ACAM1000 was just as effective as Dryvax at producing major skin reactions and at inducing immunity against vaccinia virus. The two vaccines also demonstrated equivalent safety profiles.
In some ways, however, ACAM1000 may actually be better than Dryvax. ACAM1000 'probably represents an advance over Dryvax in terms of purity, quality, freedom from bacterial contamination allowed in the old vaccine,' the authors note.
SOURCE: Nature Medicine, August 17, 2003.
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