Chlamydia is one of the most common sexually transmitted diseases (STDs) in the world. While treatable with antibiotics once diagnosed, a person with Chlamydia might not experience symptoms for months or years – if ever.

Of course, if it isn’t treated, Chlamydia can cause a huge range of problems: infertility, ectopic pregnancy (pregnancy outside the womb), and even blindness. But most people don’t even know they have contracted Chlamydia until they are tested for it.

Because of the lack of symptoms and therefore often late diagnoses, scientists have spent the last 50 or so years working on making a vaccine for Chlamydia. However, experiments had yet to yield the results they’d been hoping for.

But a team from Harvard Medical School have been working on those original experiments, developed a vaccine and carried out studies, and now they believe they have the solution!

The team found that mice injected with Chlamydia killed with UV light (ultra-violet) were more likely to contract the infection than those injected with the live bacteria. What this experiment showed was that a specific type of white blood cell called T lymphocytes were responsive to the Chlamydia bacteria.

Professor Ulrich von Andrian, an immunologist from Harvard who led the study, explained that when these T-cells are stimulated by the Chlamydia, they make what he calls “different career decisions”.

The team thought that by mixing the killed Chlamydia with adjuvants – substances that boost the immune response – it would encourage the T-cells to fight the infection. But there was no change in how the T-cells reacted.

That’s when the scientists decided to incorporate nanoparticles into the experiment. They found that with the nanoparticles attached, the adjuvants stuck to the vaccine better and ultimately protected the mice from infection. The vaccine only worked when the UV light was combined with nanoparticles, though. Otherwise, the mice were still susceptible to infection.

“We thought, perhaps we can exploit the fact that this killed Chlamydia is actually seen by the immune system,” explained Professor Andrian. “Attach a message to this killed Chlamydia, such that the response becomes the desired one.”

Professor von Andrian said that mice who were given this new and improved vaccine were able to eliminate Chlamydia even faster than those who were given the live STD and developed a natural immunity to it.

The latest studies have been published in Science and are proof of just how close we are to a vaccine that could save the world from its most common STD.