One of the most promising male birth control techniques so far has just passed another major hurdle, with trials in rabbits showing that one injection can deliver safe and effective contraception to males for at least 12 months - no condoms required.
Importantly, the results so far also indicate that the treatment, known as Vasalgel, is fully reversible, which is pretty exciting after years of condoms being the only reversible way for men to control their fertility. Human trials will begin later this year, with developers claiming it could be available to the public as early as 2018.
Developed by US-based not-for-profit company, the Parsemus Foundation, Vasalgel works by blocking the tube sperm travels down - the vas deferens - with a flexible, spongy, hydrogel material. That means all the important fluids can still get through, but larger objects, like sperm, can't, which prevents pregnancy.
Injecting Vasalgel into the vas deferens is pretty quick and easy, and the latest animal trials suggest that the contraceptive is longer-lasting than the developers had been expecting.
"Results from our study in rabbits were even better than expected," said trial leader Donald Waller, a pharmacologist at the University of Illinois at Chicago. "Vasalgel produces a very rapid contraceptive effect which lasted throughout the study due to its unique hydrogel properties. These features are important considerations for a contraceptive product to be used in humans."
There are already a host of contraceptives on the market for women - including hormonal ones like the pill, and non-hormonal ones, such as copper IUDS - but despite decades of research, the most reliable options available to men are still to use condoms or get a vasectomy, which, let's just say, aren't the most popular choices.
And given the fact that there are still 85 million unintended pregnancies each year, there's clearly room for improvement when it comes to protection.
In recent years, there have been a host of promising developments when it comes to finding ways to block men's sperm, including protein-blocking tablets, but Vasalgel has not only proven itself to be one of the most simple and effective options. It also comes with fewer potential side effects, seeing as it physically blocks sperm, rather than messing with hormones or the biochemistry of the body.
Importantly, because it's given in one long-lasting injection, it doesn't require men to take anything nightly in order to work, which has been one of factors that's reduced the effectiveness of the female contraceptive pill.
In the latest trial, 12 male rabbits were given a single injection of Vasalgel in varying doses. Eleven of the rabbits were found to be 'azoospermic' straight away, which means there were no traces of sperm in their ejaculate, and the other only had small amounts of sperm detected before also becoming azoospermic.
All 12 rabbits were unable to impregnate females throughout the year-long trial, and there were no signs of their bodies having any kind of abnormal response, the researchers report in Basic and Clinical Andrology.
Seven of the rabbits then had the Vasalgel flushed from their vas deferens, and sperm quickly returned to normal. We should notre that these particular results are pending publication, so we have to take the researchers' word for it at the moment.
That said, the results are exciting, and in addition to successful trials in baboons in 2014, have prompted the Parsemus Foundation to pursue human trials some time in 2016. With all going to plan, within two years, the product could be on the market - and while it won't protect against sexually transmitted infections, it gives couples much-needed new options when it comes to birth control.
And if you're worrying about affordability, don't. The foundation focusses on low-cost approaches that aren't patented, so are often overlooked by pharmaceutical companies because of their limited profitability. The ultimate goal is to get the cost of Vasalgel low enough to be available to all men worldwide - and keep it there.
"Contraceptive development is a hugely expensive project," said Parsemus executive director, Elaine Lissner. "But this is not just another early-stage lead; we're so close on this one. It's time to finish the job we've started."