Gaining a biologics license application (BLA) for the Phase III vaccine (ACAM2000) is a pre-cursor to Acambis securing a lucrative formal long-term "warm-base" manufacturing contract with the US government.
The contract, yet to be finalised, is expected to run for five to ten years and generate revenue of roughly £16m ($30m) a year for Acambis.
However, Acambis filed the BLA with the FDA in 2006 and in return has just received a Complete Response Letter from the FDA, asking for "additional information that it requires to complete its review."
A company press release said that the response letter was "part of the normal review process by the FDA."
Acambis spokesperson Lyndsay Wright told Outsourcing-Pharma.com that she could not comment on the nature of the extra information required, but did say that "the information and analyses requested did not require the company to perform any additional clinical testing."
According to Acambis CEO Gordon Cameron, the company is now consulting with the FDA and preparing its response, which it intends to submit as soon as possible.
The company said it expects to receive an approval response from the FDA within two and six months.
"Because there is no other licensed smallpox vaccine the approval process of ACAM2000 is being fast-tracked and at this stage we have no reason to believe the vaccine won't be approved," said Wright.
"We remain confident that we will be able to finalise and commence the warm-base manufacturing contract during 2007," said Cameron.
Interestingly, while it waits for the BLA to be approved, Acambis has already been supplying ACAM2000 to 15 governments for stockpiling under an FDA Investigational New Drug (IND) application.
The most recent of these deliveries was made in December to the US Center for Disease Control (CDC) in the form of a 10m-dose order, worth $30m, which brought the total number of doses delivered to date to 192m.
"This is a unique situation, allowing us to supply the drug before it has been approved. This is permitted by the US government under its biodefence policy introduced after September 11, as the government wants to be ready in case smallpox is used as a biological weapon," said Wright.
The aim of the warm-base contract on offer to Acambis is to ensure the firm can maintain its manufacturing capabilities and systems for the vaccine by conducting a production run every year. This will also serve to top up government stockpiles.