A new study shows that a popular form of contraception for women in eastern and southern Africa—a hormone shot administered every three months—doubles a woman’s risk of contracting HIV, The New York Times reports. The study also shows that injectable hormones used by HIV-positive women double the HIV risk for men. Roughly 6 percent of all women in sub-Saharan Africa between the ages of 15 and 49 use injectable hormones as contraception. It’s unclear how the shot increases HIV transmission risk, but researchers believe hormones in the shot appears to affect the vagina and cervix. The World Health Organization will convene in January to consider if the evidence is strong enough to advise women against using the shots as contraception.

To read the Times article, click here.