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June 21, 2002

U.S. IMMUNIZATION NEWS

"In Search of a Kinder, Gentler Vaccine"

Science (www.sciencemag.org) (05/31/02) Vol. 296, No. 5573, P. 1594; Enserink, Martin

Physicians who were present at the end of the existence of smallpox on Earth, in the 1970s in India, are concerned about the suggestion that there be widespread smallpox vaccinations before any threat of a terrorist action with the disease has been identified.  The smallpox vaccine, called Dryvax in the United States and marketed by Wyeth, usually causes a small local infection at the site of inoculation that heals within 21 days. From time to time, however, it causes progressive vaccinia, which is the vaccination grown out of control, or other side effects like eczema vaccinatum and encephalitis, both of which can be mild or fatal.  Before the end of smallpox in 1977, such reactions occurred in 1,250 out of every million people vaccinated, the majority of which were in children under two years of age.  If vaccinations were to occur today, experts believe adverse events would be much more common, because many more people today have compromised immune systems due to HIV infection and the use of immunosuppressive drugs.  A new vaccine produced by Acambis for the U.S. government, while probably not as dangerous as Dryvax, is nonetheless designed to mimic the old vaccine as closely as possible, because the old one worked, and will probably cause similar reactions.  One alternative to the currently proposed system is a primer vaccination introduced in Germany in the 1970s called modified vaccinia Ankara (MVA), a mild dose of the vaccine that helped the body adjust to it before the real vaccine was administered.  Though just 150,000 Germans took the primer, it caused no serious side effects, according to Bavarian Nordic, a company working on clinical trials of the product now.  Yet the primer and subsequent vaccination was not tested in endemic areas, and there was no outbreak of smallpox in Germany at the time against which the vaccine could be checked; in addition, it causes no mild illness and no scar at the site of inoculation, so doctors are worried that it does not offer the same protection as the traditional vaccine.  Scientists will not know if it works well unless an outbreak occurs, because conducting tests by infecting patients deliberately is unethical, yet many consider MVA unusable exactly because it has not been proven to work.

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