The much anticipated approval of Wyeth's new version of its blockbuster childhood vaccine Prevnar has been delayed by three months after the US Food and Drug Administration sought more time to review the data.

A decision had been expected end-September but the submission of more data in July covering the specifications of the chemical and physicial properties of Prevnar 13 triggered the agency request. "FDA considered this to be a major amendment and, as a result, they have elected to extend the review cycle for Prevnar 13 by 90 days," Wyeth said in a statement.

Prevnar is a vaccine designed to prevent pneumococcal disease caused by six strains of Streptococcus pneumoniae, which is responsible for a broad sweep of conditions from ear infections through to pneumonia and potentially fatal blood poisoning and meningitis. Indeed, pneumococcal disease is the leading cause of vaccine preventable death worldwide in children under the age of five and is estimated to be responsible for up to 1 million deaths in children every year.

Such has been the success of the original version of Prevnar that last year it reeled in $2.7 billion, making it Wyeth's number two drug after the antidepressant Effexor (venlafaxine). Prevnar 13 is the hugely anticipated follow up as it prevents 13 strains of Streptococcus pneumoniae and has been investigated in 13 Phase III studies involving more than 7,000 children.

"We are working closely with the FDA on the review, including conduct of the pre-approval inspections," says Emilio Emini, Executive Vice President, Vaccine R&D, Wyeth. "We continue to believe that our application supports the approval of Prevnar 13." Certainly news that the agency is already conducting inspections of the manufacturing facilities will help buffer the news for Wyeth; it also recently won its first marketing clearance for Prevnar 13 in Chile and approval is pending in more than 50 countries worldwide with more filings planned.