In the event of a smallpox outbreak, patients undergoing chemotherapy or other cancer treatments would be unable to receive the vaccine. Neither would people who have received an organ transplant or have eczema, a common skin condition.
"There's a larger population than we had anticipated, ranging anywhere from 10 to 20 million Americans," said Chimerix CEO George Painter.
The smallpox vaccine can cause life-threatening illnesses in people with compromised immune systems.
Researchers at Chimerix in Durham are developing a smallpox antidote to avoid leaving people defenseless. The antidote is an anti-viral pill that would protect people from smallpox if taken within 72 hours of exposure.
"If there were issues in getting the drug to people there's still time, post-exposure," said Painter.
He also said because smallpox is so deadly, they cannot do human clinical trials. Instead, the company will begin trials in monkeys and then submit its proposal for FDA approval.
"Given that there's not the prospect of having large human clinical trials, the development should proceed rapidly," said Painter.
The pill is a derivative of the intravenous medication Cidofovir, which has been proven effective against smallpox.
Studies show this new formulation is about 100 times more effective and does not carry the same risk of kidney problems as Cidofovir.