Researchers have found a potential breakthrough in preventing bacterial vaginosis, a condition affecting around one in three women at some point in their lives.
The infection – also known as BV – is caused by an imbalance in the bacteria that normally live in the vagina, often triggered by sex.
While it usually causes mild symptoms such as unusual discharge, BV can have serious consequences, including an increased risk of infertility, contracting sexually transmitted infections, premature birth and even newborn death.
It is routinely treated with antibiotics but can be notoriously difficult to eliminate. Around half of women see the condition return within a few months of treatment.
Now, a new clinical trial has shown that restoring protective ‘good’ bacteria in the vagina can significantly reduce the risk of the condition coming back.
The study was carried out by researchers from Mass General Brigham, the Centre for the AIDS Programme of Research in South Africa and the Vaginal Microbiome Research Consortium.
Participants were recruited from the US and South Africa. All 90 women in the trial had BV and were first treated with standard antibiotics.
After completing antibiotics, participants were randomly assigned to take either a placebo or a once-daily oral probiotic tablet containing several strains of beneficial bacteria normally found in a healthy vagina.
Researchers have found a potential breakthrough in preventing bacterial vaginosis, a condition affecting around one in three women at some point in their lives
Remarkably, even though the tablet is taken by mouth, some of the bacteria travel to and colonise the vagina.
This helps restore a healthy balance, making the environment more acidic and less hospitable to harmful bacteria – significantly reducing the risk of BV coming back.
Previous trials using a single-strain probiotic showed some promise but struggled to keep beneficial bacteria in the body for long.
The new trial, known as VIBRANT (Vaginal Live Biotherapeutic Randomised Trial), was published in Cell Host & Microbe – a leading peer–reviewed journal.
The study found that around two-thirds of women developed healthy ‘protective’ bacteria within five weeks of treatment.
Notably, some women only needed a few days of treatment for the bacteria to take hold.
They were significantly less likely to get BV again during the study.
In many cases, the beneficial bacteria were still present up to 12 weeks later – even in some women who only received a short course of the probiotic.
Unlike antibiotics, which simply clear the infection, the treatment appears to help rebuild a healthy vaginal environment that can protect itself against future infections.
The findings build on earlier research suggesting BV could in some cases be sexually transmitted.
A major Australian study, published in the New England Journal of Medicine in March 2025, found that treating both sexual partners at the same time halved recurrence rates.
‘Bacterial vaginosis is associated with not only bothersome and disruptive symptoms, but also poor reproductive health outcomes,’ said corresponding author Caroline Mitchell, director of the Vulvovaginal Disorders Program at Massachusetts General Hospital.
‘For decades, we’ve relied on medications that clear the infection but do not restore beneficial bacteria, leaving the vaginal environment vulnerable.
‘We wanted to see if we could ‘re-seed’ that environment with protective bacteria and help the body stay healthy on its own.’
Researchers say larger trials are now needed before the treatment could become widely available.
Experts say the approach could help reduce the risk of HIV, particularly in regions where both conditions are common.
Doctors have previously warned women to take steps to reduce their risk of BV.
These include avoiding perfumed soaps around the vagina and not douching (washing inside the vagina).
Other advice includes avoiding tight–fitting clothing or staying in sweaty gym wear for long periods, as this can create conditions where BV can thrive.
Using condoms during sex may also help protect the natural balance of bacteria in the vagina.
