There is only a small chance that any of the girls were infected by bats that were found in some of the sleeping shelters at Camp Potomac Woods, Loudoun County officials said.
But authorities are erring on the side of caution because about 1 percent of bats carry rabies, a viral disease that is incurable once symptoms appear. Bats can bite children in their sleep without waking them.
"We think the risk is extremely small, but we can't say there is no risk," Loudoun County Health Department Director David Goodfriend said. "Really, at the end of the day, it's the parents' decision of what level of risk they are willing to bear."
Last month, the mother of a girl who had attended the camp contacted the Girl Scout Council of the Nation's Capital. The girl had told her mother the shelter she slept in had bats living under the eaves.
Five bats subsequently caught at the camp's shelters tested negative for rabies. But officials soon learned that a few girls apparently touched a bat captured by a counselor, and some girls had not used protective netting around their beds while they slept at night.
The Loudoun health department sent letters to the parents of about 950 girls who attended the camp through July 22. Most of those contacted have declined to get the vaccine.
Health officials recommended that 16 girls begin receiving a monthlong series of shots. They include the children authorities believe were most likely to have come in contact with a bat.
The vaccine consists of six to nine shots, which can cost up to $2,000. The Girl Scouts organization is covering the cost of the shots.
Camp officials have installed screens on windows, doors and eaves in all 54 of the camp's shelters since the incident.