Researchers have published a study in Lancet Infectious Diseases showing encouraging results of an in-human study for a chlamydia vaccine, the first in the world to advance this far. If the vaccine continues to be effective through later-stage studies, it could become an important public-health tool against the most common sexually transmitted bacterial infection in the world.
"We were happy with the findings," said co-author Robin J. Shattock, Ph.D., a professor in the Department of Medicine of Imperial College London in the United Kingdom. "Vaccines -- when they are successful -- are one of the most important and effective intervention strategies we have to date."
Results of the Phase 1 vaccine study, which were published online August 12, demonstrated immune response to a new chlamydia vaccine based on the outer membrane protein of the chlamydia-causing bacteria.
The study recruited 35 women without chlamydia to see if the vaccine would provoke an immune response. The researchers split the women up into three groups: five women received a placebo saline solution, 15 women received the experimental vaccine (CTH522) combined with liposomes, and 15 received the vaccine combined with aluminium hydroxide.
Thirty-two women received all five vaccine doses, given as three injections and two intranasal boosts. All of the women who received the experimental vaccine showed signs of immune response, while none of the women in the placebo group did. Among the two versions of the vaccine, the version containing the liposome booster worked better.
Researchers determined that the liposome version produced 5.6 times more antibodies, a superior mucosal antibody profile (which helps protect against initial exposure), and an immune response profile that is typically associated with longer-acting protection.
Therefore, the authors are recommending that future research include the liposome-containing vaccine. According to Shattock, a Phase 2a study will start sometime within the next 12 to 18 months and will recruit between 500 and 2,000 women in Europe. It will be a placebo-controlled trial, and participants will be counselled about safe-sex practices, meaning the study will be large enough so that any reported infections will be statistically meaningful.
Because the vaccine is a protein-based vaccine, it would be perfectly safe to enroll patients with HIV in the study, Shattock said. Matthew Prior, M.P.H., director of communications for the National Coalition of STD Directors, added, "We would be fully in support of including the populations who bear the brunt of these epidemics" in forthcoming chlamydia vaccine trials.
Shattock said, "We would hope the vaccine would be available five to seven years from now." So far, clinical trials on a chlamydia vaccine have focused on women because chlamydia, when left untreated, can lead to pelvic inflammatory disease, infertility, or ectopic pregnancy.
Despite good diagnostic tests and effective treatments, chlamydia continues to be a major health problem worldwide. Compared to HIV, "the STD prevention toolkit is a lot thinner," said Prior.
"It's an under-funded, under-supported area of public health," he said, noting that condoms and sex education are the only meaningful prevention tools. About 131 million new cases of chlamydia are reported annually, though this is likely to be an underestimate, because many infections are symptomless.
A successful chlamydia vaccine could have other, downstream benefits, with experts noting that the inflammation caused by chlamydia makes it more likely that people will contract and transmit HIV. A study published earlier this year in the journal Sexually Transmitted Diseases found that one out of every 10 HIV infections among men who have sex with men is attributable to an existing chlamydia or gonorrhea infection.
"We know that prevention of these treatable STDs is integral towards any efforts towards ending the HIV epidemic in this country," said Prior.
Currently, chlamydia is still treatable with standard antibiotic treatment. However, experts say that an effective vaccine will become increasingly more important as chlamydia and other bacterial infections develop resistance to available antibiotic medications. With an effective vaccine, people would no longer need antibiotic treatment later in life.
"While this is a promising first step, it's still not proof that [the vaccine] works," said Shattock. "We also hope -- having been the first to get into humans -- that it will inspire others to do the same."