New chlamydia vaccine shows promise after being tested on mice

“Researchers in the United States say they have developed a vaccine that can protect against chlamydia,” The Independent reports. Initial results in mice have shown promise in protecting against this common sexually transmitted infection (STI).

Chlamydia is one of the most common STIs in the UK, and can lead to female infertility. It can also cause blindness in babies if their mother has a chlamydia infection and babies are exposed to the bacteria when they are born.

Researchers tested a new vaccine that contains ultraviolet (UV) light, which killed chlamydia bacteria when attached to tiny man-made nanoparticles – these contained chemicals that tried to enhance the immune response. When given as a spray into the nose, or directly onto the internal surface of the womb, the vaccine protected the mice against chlamydia infection. If the mice were just given UV light that killed chlamydia bacteria without attachment to the nanoparticles, this actually made them more susceptible to infection.

This is early stage research, and more animal testing is needed before the vaccine could be tested on humans. Until human studies are carried out, we won’t know whether the vaccine is safe or effective.

Currently, the most effective way to prevent catching chlamydia is considerably more low-tech than nanoparticles; always use a condom during sex, including oral and anal sex.

Where did the story come from?

The study was carried out by researchers from Harvard Medical School and other research centres in the US and Saudi Arabia, and from the pharmaceutical company Sanofi Pasteur. It was funded by the National Institutes of Health, Sanofi Pasteur, the Ragon Institute, the David Koch Prostate Cancer Foundation, and Harvard University. Some of the researchers are inventors on patent applications relating to the vaccine technology tested in the study. Some had financial interests in biotechnology companies developing this type of technology.

The study was published in the peer-reviewed medical journal Science.

The Independent covered this study well. The headline does not over-state the impact of the research; the article says the research was carried out on mice, and also includes an expert comment highlighting the early stage of the research.

The Mail Online’s subheads suggest that the vaccine is a “jab” but the vaccine actually didn't work if injected; it only worked if given via the mucous membranes, such as into the nose or womb. The Mail's headline also suggests that chlamydia is the most common cause of infertility, but this may not be correct. There are many potential causes of infertility, and in about a quarter of cases no cause can be found.

What kind of research was this?

This was animal research that aimed to test a new vaccine against chlamydia.

Chlamydia is an STI caused by the bacteria Chlamydia trachomatis. Chlamydia is one of the most common STIs in the UK, and about two-thirds of those infected are aged under 25.

In around 70-80% of women, and half of all men, chlamydia does not cause noticeable symptoms. This has resulted in widespread infection, as people do not realise they are infected, so do not seek treatment.

While symptoms of chlamydia tend to be mild (if annoying), such as pain when urinating, complications of chlamydia can be very serious, such as infertility in women.

In the developing world, it is also a common cause of blindness in babies born to women with an active infection.

There is currently no vaccine against the disease. A chlamydia vaccine was last tested in the 1960s, and although it seemed to offer some protection initially, some people who had the vaccine had more symptoms when they were exposed to chlamydia than those who were given placebo (dummy treatment). Because of this, development of the vaccine stopped.

The chlamydia bacteria infect the mucus-producing (mucosal) surfaces of the body, such as the linings of the reproductive tract. Injecting vaccines against this type of infection often does not offer much protection, because the immune response does not easily reach the mucosal surfaces. Delivering vaccines directly onto the mucosal surface has not always worked well in the past for a variety of reasons, such as not producing a strong immune response or causing side effects. The current study wanted to test a new vaccine made by attaching killed chlamydia bacteria to tiny particles called nanoparticles, given directly onto the mucosal surfaces.

This type of animal research is essential for the early testing of vaccines and drugs, to test their effects and make sure they are safe for testing on humans. While they can give an early indication of whether a vaccine may work in humans, there's no certainty until they reach human trials.

What did the research involve?

The researchers developed a new vaccine by attaching UV light-killed chlamydia bacteria to tiny man-made nanoparticles. These nanoparticles acted as biodegradable “carriers” for the vaccine and also contained chemicals that enhance immune responses, called “adjuvants”.

They compared the effect of this vaccine in mice to an infection using live chlamydia or the UV light-killed chlamydia bacteria alone. They looked at what immune response these different approaches produced, and what happened when they exposed the mice to live chlamydia bacteria four weeks later. They also compared the effects of giving the vaccine through different routes – under the skin, directly onto the mucosal surface lining the womb (uterus) or the mucosal surface lining the inside of the nose.

What were the basic results?

The researchers found that vaccinating the mice with UV light-killed chlamydia bacteria into the uterus produced a different kind of immune response to infecting them with live chlamydia. When the mice were exposed to live chlamydia bacteria four weeks later, the ones which had been vaccinated with UV light-killed chlamydia bacteria actually had worse infections (more chlamydia bacteria) than those which had been previously exposed to the live chlamydia.

However, when the researchers vaccinated the mice with UV light-killed chlamydia bacteria attached to the nanoparticles, this prompted a different immune response to UV light-killed chlamydia bacteria alone. Giving this nanoparticle vaccination through the mucosal membranes of the nose or the uterus protected the mice when they were exposed to live chlamydia bacteria four weeks later. However, giving the nanoparticle vaccination by injecting it under the skin did not work.

The researchers identified that the reason mice experienced protection when the vaccine was given onto mucous membranes was the interaction between two different types of immune system cells called memory T cells. One set of these cells remained in the mucosal tissue of the uterus, and prompted a response from the other type when exposed to chlamydia infection.

How did the researchers interpret the results?

The researchers concluded that combining UV light-killed chlamydia bacteria with nanoparticle carriers changed the immune response compared to the UV light-killed bacteria alone, and “achieved long-lived protection” against chlamydia infection.

They suggest that their nanoparticle system is an efficient way of getting vaccines onto mucosal surfaces, and might also be useful for developing vaccines against other harmful infections that target these surfaces.


This animal research has tested out a potential new vaccine against chlamydia, which utilises UV light-killed chlamydia bacteria linked to tiny nanoparticles. The vaccine did protect against chlamydia infection in mice, if it was given directly onto the mucous-producing surfaces of the nose or uterus.

Previous attempts to make a chlamydia vaccine have not been successful, and the current research also identified that this may have been due to the type of immune response produced. This new approach prompts a different immune response, including “memory” cells, which remain in the mucosal tissue. These cells prompt an immune response if they are exposed to chlamydia infection again, allowing the mice to fight the infection off more successfully.

This type of animal research is essential for the early testing of vaccines and drugs, to make sure they are safe enough for testing on humans. Humans and animals are similar enough for these studies to give an early indication of whether a vaccine may work on humans. However, it will not be possible to say for certain whether this new vaccine is effective and safe until it does reach human trials.

Chlamydia is one of the most common STIs in the UK. Although there is no vaccine currently, you can protect yourself by:

  • using a condom every time you have vaginal or anal sex
  • using a condom to cover the penis during oral sex
  • using a dam (a piece of thin, soft plastic or latex) to cover the female genitals during oral sex or when rubbing female genitals together
  • not sharing sex toys

Read more about chlamydia prevention and sexual health in general

NHS Attribution