STD Awareness: Is There a Vaccine for Syphilis?

Before antibiotics, syphilis was the most feared sexually transmitted disease (STD) out there. It was easy to get, quack cures were ineffective and often unpleasant, and it could lead to blindness, disfigurement, dementia, and even death. Syphilis rates were highest during World War II, and plummeted when penicillin became widely available later in the 1940s. By 2000, syphilis rates hit an all-time low, and many scientists thought the United States was at the dawn of the complete elimination of syphilis.

What a difference an antibiotic makes. Image: CDC

Unfortunately, it soon became apparent that syphilis wasn’t ready to go out without a fight. Since 2000, syphilis rates have nearly quadrupled, climbing from 2.1 to 7.5 per 100,000 people by 2015 — the highest they have been since 1994. If you look at the above graph, you might think syphilis rates have been pretty stable over the past 20 years — but if you zoom in, the fact that we’re in the midst of an epidemic becomes more clear.

After hitting an all-time low in 2000, syphilis rates have been increasing nearly every year since.

The epidemic is disproportionately affecting men who have sex with men (MSM), with Arizona seeing a higher-than-average syphilis rate in this group. Additionally, syphilis rates are climbing among women, who have seen a 27 percent bump between 2014 and 2015. And, since women can carry both syphilis and pregnancies, a rise in syphilis in this population also means a rise congenital syphilis (the transmission of syphilis from mother to fetus), which causes miscarriages, stillbirths, preterm births, neonatal death, and birth defects. Ocular syphilis — that is, syphilis infections that spread to the eyes and can lead to blindness — is also on the rise.

Men, women, babies — no one is immune to the grasp of syphilis.

Despite the existence of effective treatment, syphilis rates are climbing, and when the stakes are so high, perhaps we should be searching for better means of prevention. When it comes to STDs, “prevention” is usually synonymous with “condoms” — and, while condoms provide excellent protection against most STDs, they are more limited in preventing the transmission of STDs like syphilis, which are spread by skin-to-skin contact. Maybe a vaccine would be an even more effective tool for putting the final nail in syphilis’ coffin.

Treponema pallidum

Vaccines aren’t always easy to whip up, though. The bacteria that causes syphilis, Treponema pallidum, is difficult to study in the lab, as it can’t be grown in a test tube or Petri dish. T. pallidum is also very wily, with the ability to evade our immune response. Even when we’re infected naturally, we don’t develop lifelong immunity to syphilis — a trait that makes it difficult to target with a vaccine.

When I pored over the medical literature a couple of years back, I found an especially interesting example of an experimental vaccine conferring immunity in its subjects … who weren’t humans but were furry, whiskered, twitchy-nosed rabbits. These poor little bunnies were given a whopping 60 shots apiece over a 37-week period, which gave them lasting immunity to syphilis. This experiment was an interesting proof of concept that it might be possible to train the immune system to recognize the syphilis bacteria after all. However, if the prospect of having to undergo five dozen vaccinations to achieve this immunity weren’t daunting enough, here’s one more thing to bum you out: That study was published in 1973, and was the high point of syphilis-vaccine research. In the four decades since then, we haven’t been able to top that rabbit experiment.

But a new study, published in February, gives us reasons for cautious optimism. The authors tested a T. pallidum surface protein, Tp0751, to see if it would stimulate an immune response, also in rabbits — three vaccinated, and two left unimmunized for comparison. While that is a small sample size, the results were promising: While vaccinated rabbits weren’t totally immune to syphilis, they were less likely to have widespread infections that spread to other organ systems, had fewer and smaller lesions, and had stronger immune responses. Additionally, fewer bacteria were able to thrive in these rabbits.

You might be saying, “I don’t want to be poked with a needle if I’m not going to have total immunity to syphilis. What’s the point?” But even an imperfect vaccine — one that doesn’t provide total protection against infection but does help strengthen immune defenses against the spread of a syphilis infection — would be a boon for babies, as incidence of congenital syphilis could plummet in the wake of successful vaccination campaigns. And, because the spread of a syphilis infection to other organ systems is what causes so many of syphilis’ most “infamous” consequences — dementia, death, and other severe manifestations of late-stage disease — widespread vaccination could also limit the disease’s devastating effects when left untreated (such as ocular syphilis, mentioned above). And, if people’s bodies were less hospitable to T. pallidum, they might be less infectious, and therefore not as likely to transmit the disease to others.

Yes, in this study, the immunized rabbits still developed syphilis when exposed to T. pallidum. But the authors are optimistic that the vaccine can be further optimized to provide even better protection — perhaps if Tp0751 were combined with another protein called TprK, which has also shown promise in early studies. Time — and more scientific research — will tell, but it’s possible that vaccinologists will crack the code in our lifetimes.

Support for publicly funded medical research is vital, as is taking care of your own health. The CDC recommends syphilis testing for pregnant people, gay or bisexual men, and sexually active people with HIV. You can get tested for syphilis and other STDs at a Planned Parenthood health center. It’s important to catch syphilis in its early stages, as any damage it does to your body is irreversible.

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