Homeland Security

DATE=3/10/2004

TYPE=BACKGROUND REPORT

TITLE=NEW SMALLPOX VACCINE

NUMBER=5-55011

BYLINE=DAVID McALARY

DATELINE=WASHINGTON

CONTENT=

VOICED AT:

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INTRO: U-S government scientists have developed a new smallpox vaccine that has proven effective in laboratory animals, and is believed safer than the existing one. If the discovery proves safe and effective in human trials, it might become an alternative vaccine in the event of a bioterrorist attack with smallpox, as V-O-A's David McAlary reports.

TEXT: The need for a new smallpox vaccine was made clear by a recent program to inoculate U-S medical workers, police and firefighters who would have to respond to a smallpox outbreak. Among 38-thousand who received the existing vaccine, called Dryvax, last year, two percent suffered serious side effects, such as brain swelling, heart inflammation and blistery skin rashes. A U-S military study of half-a-million armed forces showed that three percent required sick leave after receiving Dryvax.

The government's top infectious disease expert -- Anthony Fauci [FOW-chee] of the National Institutes of Health -- has warned public health officials not to become complacent about the Dryvax vaccine's negative reactions.

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We cannot take this study to say that we're dealing with an absolutely safe vaccine. No. The vaccine has some severe adverse events associated with it.

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Dr. Fauci's laboratory has been working to develop a safer smallpox vaccine. Now, studies published in the journals "Nature" and "The Proceedings of the U-S National Academy of Sciences" offer hope.

The experiments show that a compound known as M-V-A (modified vaccinia Ankara) was effective against a pox virus in mice and monkeys, and had milder side effects, according to study leader Bernard Moss.

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On all counts, we found the results very encouraging. We found in both models, the mouse and the monkey, that the degree of protection was as good, or nearly as good, as the licensed vaccine. The M-V-A was perfectly safe, even when given to mice that had virtually no immune system.

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The M-V-A vaccine, like the current Dryvax preparation, is based on the vaccinia virus. When the immune system sees the organism in the vaccine, it responds as if the infection were natural and produces special disease-fighting blood cells. This trains the immune system to be ready for a real outbreak.

Dr. Moss says the difference between the two vaccines is that Dryvax produces a small infection, whereas the experimental M-V-A is highly diluted and unable to infect.

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At this point, we think the M-V-A might be used for those people recommended not to take the Dryvax. There are very large numbers of these people. There are estimates up to about 20-million in the United States.

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These include people with weakened immune systems, such as those undergoing chemotherapy for cancer, or those with the AIDS virus, H-I-V.

Another possible use for M-V-A would be as a pre-vaccine for the general population, followed by a Dryvax booster in case of a specific smallpox threat. The monkey tests show that the combination of the two vaccines offered better protection against monkeypox than M-V-A alone. Dr. Moss says, in this case, M-V-A renders Dryvax safer.

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We showed in the monkey studies reported in "Nature" that if you give M-V-A before Dryvax, then the reaction to Dryvax is much less. Just as M-V-A is able to protect against monkeypox, it also protects against a live vaccinia virus in the Dryvax.

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The next step is to conduct human trials of the new smallpox vaccine. Dr. Moss says these may take a few years, before U-S drug regulators can consider whether to approve M-V-A. (SIGNED)

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