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A chlamydia vaccine shows promise in early human trial

Chlamydia trachomatis.
Photo: Dr. E. Arum, Dr. N. Jacobs / CDC (AP)

A vaccine against the most commonly reported sexually transmitted infection in the United States – bacterial disease chlamydia – is now a significant step closer to reality. On Monday, researchers reported that two of their vaccine candidates were found to be safe in a Phase 1 clinical trial involving 35 women. Although the trial was not intended to prove their effectiveness, the vaccines also appeared to provoke an immune response to the bacteria in all volunteers.

Chlamydia trachomatis or chlamydia alone, is believed to have caused at least 127 million new infections in 2016 alone, according to the World Health Organization, a toll just for those caused by the parasite trichomoniasis. In the United States, it caused nearly 3 million new infections in 2017, according to the Centers for Disease Control and Prevention.

People with chlamydia often do not know that they have it, because many people do not experience any symptoms. But it can cause painful or bloody urination and secretion of the genitals. Failure to treat it can lead to more serious complications such as pelvic inflammatory disease, arthritis and even infertility; Carriers are also more susceptible to catching other STIs, including HIV.

Chlamydia is almost always treatable with antibiotics. But antibiotic resistance is on the horizon for it and other common STIs, including gonorrhea. So a vaccine is invaluable and especially fast. Prices of chlamydia and STI in general in the United States have steadily risen, reaching a record high in 2017.

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The two vaccine candidates, developed by scientists from the UK and Denmark, are based on the genetically engineered version of a major protein found on the surface of the bacteria. They differ in the other ingredients used to boost a person's immune response to the vaccine, known as adjuvants.

In the trial, the team dosed 30 healthy women living in the UK with one or the other vaccine (shared equally) and another five women with placebo. For a period of four months, the women were dosed three times with a shot of the vaccine or placebo, then in the last month they instead took the treatment twice through a nasal spray. At the end of the trial, 32 women had taken all five doses, although data from all women were included in the final results.

A nasopharyngeal vaccine against chlamydia, which some researchers have theorized, could better train the immune system against it, mainly because the bacteria invade areas of the body that are covered in mucus, such as our throats and genitals.

According to the team's results, published in the Lancet on Monday, there were no serious side effects from either the shot or the nasal spray. Vaccine recipients reported more irritation at the site of the shot than those taking placebo, but they reported no more side effects from the nasal spray compared to the shot.

Regardless of the vaccine taken by the women had an immune response to chlamydia, based on testing of their blood and mucus samples taken from the vagina. But one of the vaccines was packed with an experimental type of adjuvant developed by the researchers, called CAF01. Their previous research suggested that CAF01 could improve the efficacy of their chlamydia vaccine (as well as vaccines for other diseases, including tuberculosis). And in this study, the CAF01 chlamydia vaccine seemed to create a faster and more consistent immune response in volunteers.

"The vaccine showed the exact immune response we had hoped for and which we have seen in our animal experiments," said senior study Frank Follmann, director of the Department of Infectious Disease Immunology at the State Serum Institute in Denmark, in a statement from the institute. "The most important result is that we have seen protective antibodies against Chlamydia in the genitals."

The team has been working on developing a vaccine for 15 years. But with these encouraging results, they hope to gain momentum.

"Research shows that the combination of antibodies and T cells protects against Chlamydia but of course we need to test the vaccine in larger and longer-term clinical trials to see if it protects against infection. Given the results available, we have accelerated our further clinical studies, says Follmann.

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