The U.S. funds abstinence and faithfulness education in sub-Saharan Africa to prevent HIV transmission, but a new study suggests the investment doesn't lead to less risky sexual behaviors in that area.

When researchers looked at the number of sexual partners in the past year, age at first sexual intercourse and teenage pregnancy, there were no differences between countries that did or did not receive the funding.

"Changing HIV risk behaviors is hard to do, and the limited resources available for HIV prevention should be used carefully and directed towards programs that are likely to be effective," said senior author Dr. Eran Bendavid, of the Stanford University School of Medicine in California.

The U.S. President's Emergency Plan for AIDS Relief (PEPFAR) defines the components of its "ABC approach" as abstinence, be faithful and correct and consistent condom use.

Generally, the results of abstinence and faithfulness education programs are mixed, the researchers write in Health Affairs. Also, the effectiveness of these campaigns in sub-Saharan Africa remain unknown. In that part of the world, there were nearly 26 million people living with HIV in 2014, according to the World Health Organization. The region accounts for about 70 percent of new HIV infections around the globe.

Yet, PEPFAR invested more than $1.4 billion in abstinence and faithfulness programs between 2004 and 2013.

For the new study, the researchers looked at whether abstinence and faithfulness program funding was tied to changes in high-risk sexual behaviors among 477,694 people under age 30 in 22 sub-Saharan African countries between 1998 and 2013 - including 14 countries that received PEPFAR funding.

The funding did not seem to affect the number of sexual partners in the past year, age at first sexual intercourse or rates of teenage pregnancy.

U.S. studies too have found no or minimal effects of abstinence education on high-risk sexual behaviors and HIV incidence, the researchers say.

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In a statement emailed to Reuters Health, a PEPFAR spokesperson said the initiative's approach and investments have continuously evolved based on scientific evidence.

"Current prevention science demonstrates that a combination package of evidence-based behavioral, biomedical, and structural prevention interventions, tailored to the populations and geographic areas with the greatest burden, is most effective in addressing the epidemic," said the spokesperson.

Bendavid said in an email that solid evidence supports adult male circumcision, antiretroviral therapy, prevention of mother-to-child transmission and pre-exposure prophylaxis for HIV prevention.

"These are all evidence-based alternative preventive methods," he said.

The researchers say investing in evidence-backed programs could lead to improvements across the population.