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Drugs Better Than Shots for Anthrax, Study Finds

Mass immunization found to be less effective in outbreak

WEDNESDAY, Dec. 15, 2004 (HealthDayNews) -- Mass vaccination programs aimed at protecting most or all Americans against anthrax are impractical and would save fewer lives than a speedy, localized response in the event of an attack, a new report concludes.

Modeling a wide variety of hypothetical anthrax outbreak scenarios, they found that delivering vaccines and antibiotics to affected individuals within a few days of exposure may be the best way of preventing death and disease linked to anthrax.

"That's probably a much better use of resources than a massive pre-attack vaccination program," said lead researcher Ron Brookmeyer, a professor of biostatistics at Johns Hopkins Bloomberg School of Public Health.

His team's findings appear in the Dec. 16 issue of Nature.

In the more than three years since five people died and 22 more were sickened in the October 2001 anthrax attacks, policy-makers and health experts have struggled to determine the best response to any future outbreak.

One of the most talked about -- and controversial -- strategies is a nationwide, pre-exposure vaccination of most or all Americans. Concerns over possible side effects, and questions about the efficacy of the available vaccine, triggered significant resistance to a program aimed at vaccinating U.S. military personnel.

Bacillus anthracis is a microscopic spore that typically infects through either contact with the skin or, more lethally, inhalation. The vaccine currently approved for use against anthrax comes as a series of six shots delivered over 18 months. Powerful antibiotics such as ciprofloxacin (Cipro) can also beat back anthrax infection, especially if treatments begin soon after exposure.

To see whether mass immunization is, in fact, the best way to limit harm in the event of an anthrax outbreak, Brookmeyer and his team used computer modeling to simulate various scenarios. Each of the scenarios varied in terms of the amount of anthrax used, the number of people exposed, and the availability and effectiveness of vaccines and antibiotics.

According to Brookmeyer, rapid response turned out to be the most important factor in preventing disease.

"The research showed that if we could get antibiotics to people within six days of exposure, we could prevent 70 percent of cases," he said.

Even quicker response times would raise that percentage, he added.

"Is 70 percent good enough? No, we'd like to do better, so if we could shorten that period even more, we could increase the [disease] prevention rate," he said.

Surprisingly, even the best immunization programs currently available couldn't top that 70 percent rate, Brookmeyer said.

"Only the most extensive pre-attack vaccination program, one aimed at vaccinating the vast majority of people, could really increase disease prevention rates significantly beyond a more targeted, rapid response to a specific attack," he said.

"However, to achieve that high level of vaccine coverage -- immunizing that many people -- it's just not practical, we simply wouldn't be able to do it," Brookmeyer said.

On the other hand, vaccinating potentially exposed individuals after an outbreak might be of real benefit, especially if vaccine quality improves.

If vaccines were developed that could provide protection relatively quickly, "they could really shorten an otherwise very long course of antibiotics," Brookmeyer explained. He pointed out that individuals exposed to relatively large doses of anthrax must stay on Cipro or other antibiotics for up to four months, and "for a variety of reasons, we don't want people to be on antibiotics for that long."

Brookmeyer said the computer modeling also provided valuable insights into what went right -- and wrong -- in 2001.

"We did save lives in the 2001 attack -- there were cases that were definitely prevented by the use of antibiotics," he noted. "Still, some postal workers didn't receive their antibiotics until 10 or more days after exposure. We want that period shortened. If people don't get their antibiotics by at least 10 days, 50 percent of cases could still occur."

"That's the first lesson," Brookmeyer said. He believes health officials must also be prepared to disseminate smart, consistent advice to populations vulnerable to panic.

"Responding quickly is not just about detecting infection and getting drugs to those that need it," Brookmeyer said. "We in the public health community also need to have effective systems for communicating to the public and calming the public."

Dr. Nathaniel Hupert, a public health expert at Weill Cornell College of Medicine in New York City, agreed that Brookmeyer's findings point to "a role for the vaccine in reducing the need for antibiotics, but that -- as with other studies -- the use of vaccine in a pre-exposure fashion would potentially be too expensive and risky."

But Hupert added that vaccination may become important in the weeks and months following an attack, since anthrax spores can linger in the environment "for a very long time."

"If we have a large urban area that's contaminated after an anthrax [outbreak], those spores will pose an ongoing problem," said Hupert, who recently published a study assessing the response of health-care workers to the 2001 outbreak. "So even if the numbers here look bad in terms of when we should use a vaccine and what value it has, it's not the end of the story."

More information

To learn more about the causes and treatment of anthrax infection, go to the U.S. Centers for Disease Control and Prevention.

SOURCES: Ron Brookmeyer, Ph.D., professor, biostatistics, Johns Hopkins Bloomberg School of Public Health, Baltimore; Nathaniel Hupert, M.D., M.P.H., assistant professor of public health and medicine, Weill Cornell College of Medicine, New York; Dec. 16, 2004, Nature
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