Chlamydia Vaccine Clears Early Hurdle in Human Trials

A new vaccine that might prevent the spread of chlamydia, the most common bacterial sexually transmitted disease in the world, was shown to be safe and effective in a phase 1 trial. The findings, published on August 12 in the journal The Lancet Infectious Diseases, are the result of a collaboration between researchers in England and Denmark.

This initial success is important because chlamydia affects so many people around the world, says Kristin Englund, MD, an infectious disease doctor at the Cleveland Clinic in Ohio, who was not involved in the research.

“To get these positive results in the first human trials is absolutely wonderful. Hopefully this will be something that will save a lot of fertility years and a lot of pain and suffering for folks for years to come,” says Dr. Englund.

Chlamydia: 131 Million New Cases Every Year

If the vaccine is successful, it could have a huge impact on public health, says Peter Andersen, PhD, the vice president of vaccine research and development at Statens Serum Institut (SSI) in Copenhagen, Denmark, and a coauthor of the study.

Chlamydia infects 131 million people around the world each year, says Dr. Andersen.

Approximately 1,700,000 cases of chlamydia were reported in the United States in 2017, according to the Centers for Disease Control and Prevention (CDC). Although those numbers are huge, they’re probably an underestimate, says Englund. “That figure only includes the cases that are reported; it doesn’t factor in the potentially asymptomatic cases that are not being caught in screenings,” she says.

The incidence of chlamydia in the United States is also rising, adds Englund. “We’re seeing an increase of about 7 percent per year in the number of cases,” she says.

The number of reported cases of chlamydia in the United States for women is two times what it is for men: 1,127,651 for women and 577,644 cases for men. This disparity is likely due to fact that more women get screened for the infection, according to the CDC.

Although chlamydia can be treated with oral antibiotics, the majority of the people who have it are asymptomatic, and they may not know they have it, says Englund.

“Untreated, the disease can result in pelvic inflammatory disease (PID)” in women, she says. PID can cause scarring and blockages in the fallopian tubes, which can lead to infertility, chronic pelvic pain, even ectopic pregnancies, says Englund.

Phase 1 Success for a Chlamydia Vaccine Is aImportant Milestone

The controlled clinical trial was the first for a genital chlamydia vaccine and represents the latest advance in 15 years of research, according to a statement from SSI.

Thirty-five healthy women who were not infected with chlamydia were randomly assigned into three groups: 30 women received one of two formulations of the new vaccine, called CTH522, and 5 received a placebo.

The vaccination was given to participants in three intramuscular injections in the arm administered on the first day, then at 4 weeks and again at 16 weeks. Two intranasal boosts were given at 18 weeks and 20 weeks; 32 of the 35 participants received all five vaccinations.

The primary aim of the trial was to determine safety, and researchers found the vaccine to be safe and well-tolerated, with no adverse events reported. Both formulations of the vaccine provoked an immune response in all the women who received the vaccine, whereas no participants in the placebo group achieved an immune response, says Andersen.

With these findings for the phase 1 trial, the pursuit of a preventive vaccine has reached an important milestone, says Andersen. “The results are promising and there is ground for optimism,” he says, adding that many more years of research are needed before this vaccine can be marketed.

The results indicated an immunological response in the healthy women that they tested. What that response means, and whether or not it will actually be protective against chlamydia, will need to be studied in phase 2 and phase 3 trials, he says. “It’s going to take several years for this to potentially come to market, but it’s a great first step.”

Although the number of people with chlamydia suggests that the vaccine could make a big impact on world health, exactly how much benefit will depend on the price point, which for now is a question mark, says Englund. “For this vaccine to really be impactful it will need to be affordable to even resource-poor countries,” she says.

Immunizing for STDs: It’s Complicated in Spite of the Evidence

If successful and approved, how would a vaccine for chlamydia be received? The path of the HPV vaccine, which protects against certain genital types of the human papillomavirus (HPV), may provide clues.

The vaccine for HPV has made a significant impact on reducing the prevalence of the infection and genital warts, according to a meta-analysis published on August 10, 2019, in The Lancet. It’s included in routine vaccinations (at least for girls and women) in 71 countries, as is recommended by the World Health Organization.

Still, the vaccine has generated some controversy ever since it was first approved, in 2006. Many believed that the vaccine would promote or at least give passive permission for teens to engage in sex. Would a vaccine for chlamydia face similar resistance?

Both vaccines are medically important, says Englund. “With HPV, you can get cancer, and with chlamydia, you can have long-term impacts on fertility and pain. I think people can probably wrap their heads around the immediate impact of chlamydia more than they can for HPV,” she says. It can be more difficult for people to understand and really appreciate the long-term effects of HPV and the risk of cancer, she adds.

RELATED: Public Health Officials Push for More Effort Vaccinating Kids Against HPV

Controversy around protections for sexually transmitted diseases are often based on misconceptions, notes Englund. “It’s a myth that if you vaccinate someone against a sexually transmitted infection like HPV or potentially like chlamydia, they may get the feeling that they’re safe and it may encourage them to have unprotected sex. We’ve really not seen that with anything else,” she says.

Englund says we need to get away from stigmatizing these vaccines as promoting promiscuity, because they haven’t been shown to increase the likelihood that people will become more sexually active.

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