This publication spoke with the lead researcher on the study‚ American epidemiologist Dr Chelsea Polis.

It is important to note: a 40% increased risk doesn’t mean a 40% chance of getting HIV.

Q: Can you explain what increased risk means?

Polis explained: For example‚ based on the current HIV incidence rates in South Africa‚ a woman aged 15 to 24 who is not using Depo-Provera has about a 2.4% chance per year of contracting. If it does increase her risk by 40%‚ then using the hormone would increase her average chances of getting HIV to about a 3.3% chance per year.

Q: What is the risk for women living in areas of high HIV prevalence?

Polis explained that a woman in a low-income country having condom-less vaginal sex once a week with an HIV-positive male partner‚ who is not using antiretroviral therapy‚ has about a 14% chance per year of contracting HIV.

If the injection increases the risk of HIV acquisition by 40%‚ then using the injection would increase her average chances of getting HIV to about 19% per year.

Q: So what can women do?

According to the World Health Organisation‚ women should be given information on all the benefits and risks of different forms of contraceptives and be advised to use condoms during sex.

Polis explained that women should be made aware that Depo-Provera may potentially make her more vulnerable to contracting HIV if she is sexually active and has an HIV-positive partner‚ but the possibility is not 100% conclusive.

"She should be assisted to consider what this means in the context of her individual circumstances‚ and should be permitted to decide whether she would prefer to use this option‚ ideally in conjunction with a condom‚ or opt for an alternative method."

Q: The evidence of increased risk in humans is not conclusive‚ so what do people make of this?

Polis said: "This concern should neither be dismissed as unimportant‚ nor used to cause undue panic by failing to appropriately contextualise the issue or to understand the underlying evidence."

Q: What should countries do?

Polis said countries have to weigh up reducing the distribution of Depo-Provera contraceptive injections with the risk of "potential increases in unintended pregnancy and maternal/infant morbidity and mortality".

Polis on Twitter pointed to the study in journal Global Health: Science and Practice‚ which did modelling to look at what would happen if the injection were to be removed from Sub-Saharan Africa.

The study found it would be too difficult to change all people in Sub-Saharan Africa to different contraceptives and maternal mortality deaths would spike‚ as would unwanted children.

In the meantime‚ scientists are awaiting the results of the randomised control ECHO trial being conducted in South Africa‚ Zimbabwe and Kenya‚ which looks at this injection versus two other forms of contraception to see if it leads to an increased risk of HIV.