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Last Updated

15 Jul 2003

Source: Wall Street Journal, July 15, 2003


NIH Study Points to Vaccine For Smallpox That's Safer


Scientists at the National Institutes of Health took a step toward a safer smallpox vaccine by demonstrating that two experimental vaccines with a lower risk of side effects were equally effective as the currently approved product in preventing pox infection in test mice.

Millions of Americans are now considered too high-risk to receive the standard Dryvax vaccine, made by Wyeth, because their immunity is weakened by HIV/AIDS, organ transplant, or cancer chemotherapy. Still others are excluded due to eczema, a common skin rash. Adverse reactions include widespread pox, encephalitis and in rare cases, death.

Fear of the vaccine's dangers helped scuttle the nation's plan to vaccinate 500,000 U.S. health workers to protect against a bioterror strike. As of July 4, only 38,000 -- less than one-tenth the original target -- had volunteered. While most side effects were limited to fever or rash, at least seven cases of cardiovascular disease, including one death, occurred.

Amid increasing urgency of finding a second-generation vaccine, the NIH scientists reported that they successfully immunized mice with vaccines based on milder strains of vaccinia virus. One of the vaccines is called modified vaccinia Ankara, or MVA, and the other is known as NYVAC. Both MVA and NYVAC provided the same protection against smallpox infection as Dryvax after intentional exposure to a lethal strain of vaccinia.

"This is very encouraging news," said Igor Belyakov, senior scientist at the National Cancer Institute, first author of the report published in Tuesday's issue of the Proceedings of the National Academy of Sciences.

"Everybody is very anxious to get a vaccine that doesn't have the complications of Dryvax," said Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, an arm of the NIH involved in the study. Dr. Fauci called the study "the first step in the direction of showing it would be effective in humans for smallpox."

Another finding from the study: The safer vaccines worked as well when given intranasally as when injected. Intranasal vaccine is believed promising for smallpox, since it puts protection right at the site where the virus infects its victims when inhaled into the respiratory tract.

A third discovery: Blocking pox infection required strong antibody response, and the vaccine boosts antibodies. But when pox cases occurred, only test animals with another immune-system component, a strong T-cell defense, survived. Since AIDS patients often lack T-cells, this finding further increases urgency of finding a vaccine for them to boost antibodies and prevent infection.

Smallpox researcher Peter Jahrling, a virologist at the U.S. Army Medical Research Institute of Infectious Diseases, called the PNAS study "elegant," and its insight into antibody protection "surprising and counterintuitive, but very important." Dr. Jahrling wasn't involved in the PNAS paper, but added that his own monkey studies also look "very promising."

Study author Dr. Belyakov said further experiments may involve a prevaccination with MVA followed by Dryvax, to see if the safer vaccine can lessen the inflamed bump that normally erupts at the injection site, and mute other adverse effects of Dryvax.

MVA has long been viewed as safe, after it was used to vaccinate about 150,000 German citizens in the mid-1970s. But it wasn't developed in the U.S. then because the U.S. had already halted its vaccination program.

More recently, however, MVA has been researched by Therion Biologics Corp. of Cambridge, Mass. And another biotech company, VaxGen Inc., of Brisbane, Calif., has been probing a different candidate for a safer smallpox vaccine.