Canadian scientists have developed a promising vaccine prototype against chlamydia, a study in mice suggests.
Research, published in the journal Vaccine, shows that mice given the immunisation are more likely to fight off the infection.
Chlamydia is one of the most common sexually transmitted infections in the UK and globally. There is currently no vaccine approved for human use.
Experts say condoms are currently the best form of protection.
A team of researchers at McMaster University in Ontario gave mice two doses of the prototype vaccine, delivered through the nose.
When the animals were later exposed to chlamydia, vaccinated mice had fewer copies of the bacteria replicating in their systems.
Mice in the vaccinated group also had fewer signs of damage to their reproductive organs.
Prof James Mahony described the results as "very promising".
He added: "We will trial the vaccine on other animal models before moving on to human trials."
Researchers hope their vaccine will also work against chlamydia infections of the eye - a common cause of blindness in developing countries.
Meanwhile, figures released by Public Health England suggest chlamydia was the most common sexually transmitted infection last year.
There were more than 200,000 diagnoses of chlamydia in 2015, with 129,000 among young people aged 15 to 24 years.
The infection is most commonly passed on through sexual contact but often people do not notice any symptoms.
However, if not treated with antibiotics early on, the bug can lead to long-term health issues such as pelvic inflammatory disease and infertility.
Public Health England says anyone under 25 who is sexually active should be tested for chlamydia every year and when they change partners.