WASHINGTON (Reuters) - Circumcision may help protect men from the AIDS virus but it does not protect the wives and female partners of infected men, researchers reported on Thursday.

The disappointed researchers had to stop the trial, which they had hoped would confirm early suggestions that circumcision would protect men and women alike.

But, they said, circumcision is so effective in protecting men that will still likely benefit women indirectly by reducing circulation of the virus in general.

“We were disappointed that the trial did not show protection from HIV infection in women, as was expected from observational studies,” Dr. Maria Wawer of Johns Hopkins University in Baltimore and colleagues in Uganda wrote in the Lancet medical journal.

“The trial was stopped early because of futility.”

AIDS is caused by the fatal and incurable human immunodeficiency virus and is transmitted mostly through sex. It has killed 25 million people since it was identified in the early 1980s and infects an estimated 33 million.

Most cases are in Africa, passed along mainly by sex between men and women. Researchers have demonstrated several times that men who are circumcised are less likely to become infected by female partners.

The foreskin of the penis, which is removed during circumcision, is rich in cells that are particularly easy for the virus to infect. The theory is that removing this source of vulnerable cells makes infection more difficult.

Wawer’s team recruited 922 uncircumcised, HIV-infected, men aged 15 to 49 years. Some were immediately circumcised and some had the procedure delayed for two years.

The researchers also followed 163 wives or female sex partners of these men.

“Circumcision of HIV-infected men did not reduce HIV transmission to female partners over 24 months; longer-term effects could not be assessed,” Wawer’s team wrote.

“Condom use after male circumcision is essential for HIV prevention.”

The sex partners of circumcised men also were no less likely to get other sexually transmitted infections with the exception of one called trichomonas.

“However, the efficacy of male circumcision for prevention of HIV in uninfected men is clear, and reductions in male acquisition of HIV attributable to circumcision are likely to reduce women’s exposure to HIV-infected men. Male circumcision programs are thus likely to confer an overall benefit to women,” the researchers concluded.