The first ever global study of Group B Streptococcus has revealed that more than 20 million pregnant women carry the bacteria and most of them are currently unidentified and untreated.

Researchers have also found that a vaccine may prevent 231,000 infant and maternal cases.

An estimated one in five pregnant women around the world carry Group B Streptococcus (GBS) bacteria which is a major, yet preventable, cause of maternal and infant ill health globally.

More than 100 researchers from around the world took part in the study which was funded by the Bill & Melinda Gates Foundation and includes data and estimates for the year 2015 from every country of the world, including outcomes for pregnant women, their babies and young infants.

The research estimates that out of 410,000 GBS cases that occur globally every year, there will be at least 147,000 stillbirths and infant deaths.

Paul Heath, professor of paediatric infectious diseases at St George’s, University of London, who was a member of the Expert Advisory Group for the new research, said: “This comprehensive work provides major insight into the burden of GBS globally and emphasises the pressing need for the development of an effective Group B Strep vaccine.”

Previous data on GBS burden focused on infant cases and high-income countries, but the impact of GBS disease worldwide, especially in Asia, was less clear.

The new research found GBS is present among pregnant women in all regions of the world, with an average of 18% of pregnant women worldwide carrying (colonised with) the bacteria, ranging from 11% in eastern Asia to 35% in the Caribbean, totalling 21.7 million in 195 countries.

Although several vaccines to prevent GBS are in development, none is currently available. This is despite the disease accounting for more than the combined neonatal deaths from tetanus, pertussis, and respiratory syncytial virus, for which maternal vaccines are already in use, or further advanced in development.

This analysis shows for the first time that a maternal GBS vaccine, which was 80% effective and reached 90% of women, could potentially prevent 231,000 infant and maternal GBS cases.

GBS is carried by up to a third of adults, usually with no symptoms. In women, GBS can live harmlessly in the digestive system or lower vaginal tract, from where it can be passed to the unborn baby through the amniotic fluid or to newborns during labour.

Babies are more vulnerable to infection as their immature immune systems cannot fight off the multiplying bacteria. If untreated, GBS can cause serious infections, such as meningitis and septicaemia, can lead to stillbirths, and can cause newborn and infant deaths. If they survive, babies can develop permanent problems including hearing or vision loss, or cerebral palsy.

Current GBS prevention focuses on giving antibiotics to women in labour, aiming to reduce disease in infants at delivery. At least 60 countries have a policy for antibiotic use in pregnancy to prevent newborn GBS disease.

Dr Keith Klugman, Director of the Pneumonia Team at the Bill & Melinda Gates Foundation, said “The first few days and weeks of a baby's life are the most vulnerable - by far.

“By filling in one of the great voids in public health data, this work provides crucial insight and shows the pressing unmet need for the development of an effective Group B Strep vaccine.

“Immunising expectant mothers is a potentially ground-breaking approach that could dramatically reduce the number of maternal and child deaths.”

Johan Vekemans, co-author and Medical Officer, Initiative for Vaccine Research, World Health Organization, said: “These disease burden estimates highlight the importance of perinatal infection prevention. Existing recommendations should be implemented, but these are insufficient, and the number of affected families r