STD Awareness: The Long Road to a Chlamydia Vaccine

Earlier this year, television personality John Oliver was the butt of an elaborate prank orchestrated by actor Russell Crowe. It started with an auctioned jock strap, and ended with Crowe funding the John Oliver Koala Chlamydia Ward at the Australia Zoo. If you want the full story, check out the video below (beware explicit language).

Despite Oliver playing it for laughs, koala chlamydia is very real and very serious. At least half of wild koalas are infected with a chlamydia type that’s related to the human version. As in humans, koalas can transmit these bacteria through sexual contact. And, similar to the havoc it wreaks in our species, in koalas chlamydia can cause blindness, urinary tract infections, and female infertility — and can be passed from mother to infant. Along with other factors, chlamydia is said to be responsible for plummeting koala populations in many parts of Australia.

The good news is this crisis in the koala community is spurring action from the scientific community, and Australian researchers are busy developing a chlamydia vaccine for koalas. The hope is that, someday, koala populations can bounce back with appropriate disease control and other conservation measures.

But what about humans? For millennia, our species has been vexed by Chlamydia trachomatis, the bacteria that cause chlamydia. And even as we started figuring out how to immunize against other diseases, chlamydia kept eluding our attempts at vaccination. But a vaccine sure would be handy. After all, Americans spend more than half a billion dollars every year dealing with their chlamydia infections. Worse than that is the human cost: Chlamydia can cause infertility, and can be passed from mother to infant to cause infections and blindness. Most worrying, the fact that it often doesn’t cause symptoms means people might not seek treatment, allowing the bacteria to cause behind-the-scenes damage in the reproductive system.

Luckily, we’re starting to make some headway in our quest to conquer chlamydia. But it’s been a long, long road. The first chlamydia vaccine to be tested in humans was developed more than a century ago, but the bacteria proved to be a tough nut to crack. Last year, the first human trial in half a century was completed, but results haven’t yet been published. And it was only a phase I trial — a small experiment designed to learn if the vaccine is safe. If this vaccine candidate advances to larger trials, only then will it be assessed for effectiveness.

But research into a chlamydia vaccine is chugging along for another species. For example, in 2015, Science described a newly developed chlamydia vaccine that showed promise in mice. The following year, a separate team started building on other mouse studies, harnessing high-tech tricks to circumvent Chlamydia trachomatis‘ wily ways. And a year ago, creating cause for celebration among needlephobes, other researchers stumbled upon clues that preventive chlamydia vaccines might be more effective if administered orally rather than by a shot — at least in mice.

Indeed, the lion’s share of research into chlamydia vaccines has been performed in mice — a species that is separated from humans by about 100 million years of evolution, and doesn’t exactly mimic the human body. A joke I’ve heard from more than one scientist: “We can cure any disease … in mice.” Animal studies, unfortunately, often prove to be experimental dead ends — as evidenced by a century’s worth of research into chlamydia vaccines with nothing on the market to show for it. But there are reasons for optimism — for example, just less than a decade ago, we figured out how to play with the bug’s genes, opening up new avenues of research.

Developing a chlamydia vaccine might not seem as urgent a priority as a vaccine against a deadly disease with no cure, like HIV, or a disease that’s rapidly evolving resistance to treatment, like gonorrhea. But, with antibiotic resistance representing a growing concern today, many researchers would rather vaccinate common bacteria out of existence than allow them to continue to plague us — and evolve more tricks for protecting themselves against the drugs that are supposed to kill them.

A colony of C. trachomatis (in green) nestled inside a human cell. Image: V. Brinkmann, Max Planck Institute for Infection Biology

So, until chlamydia can be prevented with a vaccine, we need to make sure our cures remain effective. Last month, a team published findings that could help us get more bang for our buck from antibiotics. They uncovered some of the tricks Chlamydia trachomatis has up its sleeves, enabling it to hide from our immune systems — and hope to find drugs that strip the bacteria of their ability to hide in plain sight. No longer able to evade our immune systems, our body’s defenses might be able to do a better job on their own, raising the possibility that chlamydia could be cured with lower doses of antibiotics — or none at all.

Yes, antibiotics are the wonder drugs of the 20th century and have saved untold lives, but they can become less effective as the microbes they target learn to outmaneuver them. Plus, antibiotics can do collateral damage by killing off “good” bacteria that keep us healthy, disrupting our bodies’ ecosystems and making us more vulnerable to other maladies, like diarrhea and yeast infections. We’re only just beginning to understand how communities of beneficial microbes in our bodies contribute to our health, but it’s becoming clear that antibiotics should be conserved rather than handed out willy-nilly.

The best way for sexually active people to protect themselves from chlamydia is to practice safer sex and know their partner’s status. You can be tested and treated for STDs or pick up condoms at any Planned Parenthood health center.

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