May 1, 2006

Vaccine Plus Antibiotics Protects Against Anthrax

By Maggie Fox, Health and Science Correspondent

WASHINGTON -- Combining an anthrax vaccine with a short course of antibiotics completely protected monkeys who inhaled spores of the often-deadly bacteria, offering perhaps a more realistic way to protect people in case of a biological attack, researchers said on Monday.

The finding suggests it may be possible to vaccinate people who have been exposed to anthrax spores, and give them a short, two-week course of antibiotics to provide extra protection while their immune system gears up, the researchers report in this week's issue of the Proceedings of the National Academy of Sciences.

This could be a more useful way to treat people who are exposed to inhaled anthrax than the current regime of taking antibiotics every day for two months, the team at the U.S. Army Medical Research Institute of Infectious Diseases and the National Institute of Allergy and Infectious Diseases said.

"This provides direct evidence that the combination of anthrax vaccine with a short course of antibiotics given post exposure can completely protect nonhuman primates from inhalational anthrax," said Dr. Arthur Friedlander, who led the study.

"Our results also suggest that the appearance of an antibody response -- after treatment with antibiotics alone or in conjunction with vaccination -- might be useful in determining when antibiotics can be safely discontinued."

In October 2001, someone sent several letters contaminated with anthrax spores to several U.S. offices, including at the Senate in Washington.

Eleven people became infected with inhalational anthrax, the most deadly form, and five of them died. No one has ever been charged with the crime.


Inhaled anthrax is dangerous because it can form spores that lodge in the lungs and become dormant weeks after the initial exposure.

If someone knows he or she has been exposed, anthrax is easily treated with antibiotics, but once the symptoms of inhaled anthrax begin it is almost impossible to treat because the bacteria have already pumped out lethal amounts of toxin.

So after the 2001 attacks, more than 10,000 people who may have been exposed to the spores, notably employees of the U.S. Senate and some postal workers, were offered a 60-day course of ciprofloxacin or doxycycline, the two antibiotics that can prevent anthrax symptoms.

But it is difficult to take antibiotics for such a long time and there are significant side effects.

"Adverse events associated with antibiotic prophylaxis such as diarrhea, nausea, vomiting, and dizziness were commonly reported," the researchers wrote.

"More importantly, the overall adherence rate during 60 days of antibiotics was poor (44 percent)," they added.

So the researchers tested two groups of 10 rhesus macaques each, exposing them to a lethal dose of anthrax spores and then giving them 14 days worth of antibiotics.

"One group also received three doses of the licensed human anthrax vaccine," the researchers wrote.

Only four monkeys given antibiotics alone lived, compared to all 10 who got the vaccine also.

And the animals were immune to anthrax eight to 11 months later, suggesting long-term benefit from the vaccine, the researchers said.