ATLANTA (AP) -- British drug maker GlaxoSmithKline PLC said Monday that its cervical cancer vaccine produced an immune response to viruses associated with cancer in all women in a late-stage clinical study.

In a Phase III study, 666 women aged 15 to 55 were vaccinated with the company's Ceravix cancer vaccine. After a month of treatment, all women showed antibodies to type 16 and type 18 human papillomavirus, strains of the virus that are associated with cervical cancer. Antibody levels were assessed after 7 months and 12 months of treatment.

Results also suggested that women over the age of 25 may be better protected from infection from the viruses. The company found that women over the age of 25 had antibodies level greater than or equal to women aged 15 to 25.

American depositary shares of GlaxoSmithKline fell 1 cent to $55.98 in morning trading on the New York Stock Exchange.