TRENTON, N.J. – Drug maker (NYSE: WYE) said Tuesday that U.S. approval of a much-anticipated, improved version of its blockbuster children’s vaccine Prevnar has been delayed.

If approved the vaccine would be manufactured at Wyeth’s massive plant in Sanford, N.C. as well as two other locations, according to a company spokesperson.

Wyeth had expected a ruling by Sept. 30 from the Food and Drug Administration on whether it can start selling Prevnar 13.

The vaccine reduces risk of infection by 13 strains of pneumococcal disease, which causes many ear infections and potentially deadly meningitis, pneumonia and blood infections.

That’s six more types of the bacterial disease than are prevented by the current vaccine, Prevnar, which had $2.7 billion in sales last year. Prevnar is Wyeth’s No. 2 product by revenue, behind antidepressant Effexor.

Wyeth, based in Madison, N.J., said that in late July it sent FDA additional information about analysis of and specifications on the physical and chemical properties of Prevnar 13. That was in response to an FDA request.

The agency then decided that was a major amendment to Wyeth’s application for approval of Prevnar 13, and so extended the review period for the vaccine by 90 days to Dec. 30, Wyeth said.

Such FDA delays have become common the last few years.

Wyeth is seeking FDA approval to market the vaccine for infants and young children and has tested it in more than 7,000 youngsters in 13 major studies.

Pneumococcal disease is the top vaccine-preventable cause of death worldwide in children younger than 5 and leads to an estimated 5 million deaths among children each year.

"We are working closely with the FDA on the review," Emilio Emini, Wyeth’s head of vaccine research and development, said in a statement. "We continue to believe that our application supports the approval of Prevnar 13."

Wyeth applied for approval of Prevnar 13 on March 31 and on May 7 was granted a priority review, a designation indicating the FDA sees a potential product as a significant public health advance.

Wyeth spokeswoman Natalie de Vane said the FDA already is inspecting the three factories where Wyeth would manufacture the vaccine: Sanford’ Pearl River, N.Y., and Grange Castle, Ireland, the company’s main site for making biological products, those produced in living cells.

"They’re going well," she said of the inspections. "It’s an indication that things are moving along at a good pace."

Prevnar has been on the market for more than nine years and is on sale in 95 countries. More than 235 million doses have been distributed.

The vaccine requires a series of four injections, generally given at 2, 4 and 6 months old and then between 12 and 15 months old.

Prevnar 13 recently got its first approval, in July in Chile, where it is known as Prevenar 13. Approval is pending in more than 50 countries besides the U.S.