Rapidly distributing antibiotics to people exposed to
anthrax spores during a bioterrorist attack could, by
itself, prevent about 70 percent of anthrax infections,
according to researchers from the Johns Hopkins
Bloomberg School of Public
Health.
To increase the prevention rate to 90 percent, their
study found that at least 63 percent of the population
would need to be immunized with vaccine before an anthrax
attack, which might not be practical. However, the study
found that anthrax vaccination given even after an attack
could be beneficial in reducing the length of time
antibiotic treatment would be needed. These findings could
be an important tool for policy-makers who must develop
effective strategies for containing an anthrax outbreak.
The study is published in the Dec. 16 edition of
Nature.
The Johns Hopkins researchers developed a probability
model to predict how many cases of anthrax could be
prevented under varying conditions. The study found that
about 70 percent of anthrax cases could be prevented if
antibiotics were distributed within six days after exposure
and patients were to take them for 60 days. Prevention
rates dropped below 50 percent if antibiotics were delayed
more than 10 days. In 2001, some postal workers did not
begin taking antibiotics until nine days after exposure.
The current licensed anthrax vaccine requires six
doses over an 18-month period to provide immunity. The
researchers looked at what impact a new and improved
anthrax vaccine could have and evaluated a range of vaccine
characteristics that could begin to provide immunity
ranging between seven and 28 days. When vaccine was
distributed along with antibiotics after an attack, the
researchers calculated that vaccine prevented few
additional cases from occurring when compared to just rapid
use of antibiotics. However, they found that if the vaccine
is 95 percent effective, it could reduce the time that
antibiotics would be needed by up to 43 days.
An 80 percent effective vaccine could reduce time on
antibiotics by up to 23 days. The vaccine also could
prevent cases if an antibiotic-resistant strain of anthrax
were used in an attack.
"Our study highlights the need for rapid distribution
of antibiotics to minimize casualties from an anthrax
outbreak," said Ron Brookmeyer, lead author of the study
and professor in the
Department of
Biostatistics. "But a long course of antibiotics is not
ideal, and a new, improved anthrax vaccine could be
especially helpful in reducing duration of antibiotic
treatments."
The study was written by Ron Brookmeyer and Elizabeth
Johnson, in Biostatistics at the Bloomberg School, and
Robert Bollinger, in the Division of Infectious Diseases at
the School of Medicine. The research was funded by the
Fogarty International Center and the National Institute of
Allergy and Infectious Diseases.