Is there a chlamydia vaccine?

The first major attempt at a vaccine against chlamydia has passed a hurdle. Chlamydia is the most common reportable bacterial sexually transmitted infection (STI). While it’s asymptomatic in most people, it can cause serious complications for women, so a vaccine in progress is good news. Read on to learn more about this encouraging development. 

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Chlamydia is an STI caused by the bacterium Chlamydia trachomatis that is often unrecognized because most people don’t have any symptoms. If left untreated, chlamydia can lead to pelvic inflammatory disease (PID) in women. PID causes inflammation of the female reproductive organs, including the uterus, fallopian tubes, and ovaries. PID may also result in scarring or blockage in the fallopian tubes, which can lead to chronic pelvic pain, infertility, or a potentially fatal ectopic pregnancy. 

In men, chlamydia can lead to urethritis (inflammation of the urethra), prostatitis (inflammation of the prostate gland), epididymitis (inflammation of the coil of tubes attached to the back of the testicles) (Hsu, 2019).

A vaccine is a treatment that sensitizes a person's body to a particular disease, helping protect against acquiring that specific disease in the future. It often takes years of research for new vaccine development.

For now, there is no vaccine for chlamydia; however, there may be one in the coming years if further clinical trials show it to be safe and effective. In a recent issue of The Lancet Infectious Diseases, researchers reported that two versions of a chlamydia vaccine were found to be safe as part of a Phase 1 trial. Phase 1 human trials are done in very small groups of people (in this case, 35 healthy women) and look at safety and side effects (Abraham, 2019). 

In this study, the potential vaccine candidates for chlamydia were deemed safe and well-tolerated, which means they could eventually move on to the next phase of clinical trials. Researchers also found that the chlamydia vaccines provoked an immune response against the STI—with no such response in the placebo group. The main side effect was a local reaction at the injection site. While these results are promising from a public health standpoint, more clinical trials are needed (Abraham, 2019).

Chlamydia is one of the most common STIs, with an estimated 131 million people infected worldwide each year. In the United States, it’s the most frequently reported STI caused by bacteria. The Centers for Disease Control and Prevention (CDC) estimate that approximately four million cases occurred in 2018—most infections go unreported because of vague or nonexistent symptoms (CDC, 2021). 

Chlamydia is particularly common in younger people. According to the CDC, 1 in 20 sexually active young women between the ages of 14 and 24 are infected with the bacterium. Because chlamydia often has no symptoms, many men and women with chlamydia may not know it, passing the infection to new partners or failing to get the necessary treatment. Antibiotics can easily cure chlamydia (Torrone, 2014).

20–30% of genital chlamydia infections in women lead to symptomatic pelvic inflammatory disease (PID). Some women with PID will develop infertility, pelvic pain, and potentially dangerous ectopic pregnancies (Park, 2017). 

Chlamydia can cause complications in men, although they're far less frequent. Complications can include prostatitis (inflammation of the prostate) or inflammation of the urethra (urethritis). Around 1% of biological males who have urethritis may develop reactive arthritis. In some cases, urethritis and reactive arthritis also occur with eye inflammation. This triad of symptoms (arthritis, urethritis, and eye inflammation) is called Reiter's syndrome (Hsu, 2019). 

In most cases, chlamydia has no symptoms.

In women, chlamydia usually infects the cervix first, causing cervicitis (inflammation of the cervix). That can cause pain, irritation, or vaginal discharge. Chlamydia infections can also involve the urethra, leading to urethritis and causing pain while urinating (Hsu, 2019).

In men, chlamydia bacteria can infect the urethra and lead to urethritis (inflammation of the urethra), which causes pain while urinating and urethral discharge. Untreated chlamydia infection can also cause epididymitis, swelling in the tubes on the back of the testicles, causing pain (Hsu, 2019).

In both women and men, chlamydia can infect the eyes, causing chlamydial conjunctivitis (a type of eye inflammation)—symptoms include redness, irritation, and tearing. Chlamydia can also infect the rectum, either through anal sex or the spread of bacteria from the vagina. This might produce pain, discharge or bleeding, or no symptoms at all (Hsu, 2019).

Chlamydia trachomatis is also responsible for lymphogranuloma venereum (LGV), an infection of the lymphatic system, causing tender, swollen lymph nodes. It can also cause inflammation in the rectum accompanied by gastrointestinal symptoms (Hsu, 2019).

While we aren’t there yet, it looks like there may be hope for a chlamydia vaccine in the near future. Researchers are particularly encouraged because of the success of the vaccine against another common STI, human papillomavirus (HPV). Hopefully, further trials and vaccine research will lead to a genital chlamydia vaccine. 

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Current version

May 11, 2021

Written by

Michael Martin

Fact checked by

Mike Bohl, MD, MPH, ALM

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About the medical reviewer

Mike Bohl, MD, MPH, ALM

Dr. Mike is a licensed physician and a former Director, Medical Content & Education at Ro.