The Centers for Disease Control and Prevention said Friday that fewer doses of the H1N1 vaccine will be available by the end of the month because the vaccine is taking longer to make than expected.

The CDC had hoped that manufacturers would be able to make 40 million doses by the end of the month.

Anne Schuchat, the director of that National Center for Immunization and Respiratory Diseases at the Centers for Disease Control and Prevention, said it appears the 40 million-dose estimate will be reduced by 10 million to 12 million doses. However, she said the doses should be available by the beginning of next month.

The production process involving the antigen, or active ingredient, used in the H1N1 vaccine has been slower than usually seen with seasonal vaccines. Viruses for both vaccines are grown in chicken eggs before going through a purification process.

Schuchat said the vaccines also need to undergo various tests before the FDA signs off on their release.

She also said that 86 children have died from the H1N1 flu, with 43 of the deaths coming in the last month. Schuchat said there's usually about 40 to 50 pediatric deaths from seasonal influenza over an entire flu season, so the H1N1 death rate in children is higher.

The CDC said 41 states reported widespread influenza activity during the week that ended Oct. 10, which the agency said is unusual for this time of year.

The U.S. has purchased 95 million H1N1 vaccines and enough bulk ingredients from five companies to make up to make a total of 251 vaccine doses if needed. The vaccines are being distributed to states and some large cities, which in turn will distribute the vaccines to about 90,000 health-care providers, retailers and local health departments over a period of several weeks.

MedImmune, which is a unit of AstraZeneca PLC (AZN), makes a mist that's delivered through the nose and is approved for "healthy" people ages 2 to 49. It's not approved for use by pregnant women, who have also been hit hard by the H1N1 flu.

Other companies, including a unit of Sanofi Aventis (SNY), Novartis AG (NVS), CSL Ltd. (CSL.AU) and GlaxoSmithKline PLC (GSK), are making H1N1 flu shots for the U.S. market. Glaxo's vaccine is still pending FDA approval.

-By Jennifer Corbett Dooren, Dow Jones Newswires; 202-862-9294; jennifer.corbett@dowjones.com