Group B streptococcus vaccine estimated to prevent 1...

"Streptococcus vaccine could prevent over 100,000 baby deaths worldwide," The Guardian reports.

Group B streptococcus (GBS) is a common bacterium that around 1 in 5 women carry (usually harmlessly) in the vaginal tract. However, it can sometimes be transmitted to babies during childbirth and cause infection in the newborn.

The study estimated global infection rates among mothers and newborns in 2015 and the impact this has across the world. It estimated that worldwide about 15% of babies born in 2015 were exposed to GBS, and about 1.5% of these exposed newborns developed a GBS infection. A large proportion of these infections and the resulting complications occurred in developing regions such as Africa and Asia, which have poorer access to healthcare.

The researchers further estimated that giving antibiotics to high-risk women during delivery (which is already done in some countries) could prevent about 40% of infections. Giving a GBS vaccine to all women could potentially prevent as many as 70% of infections.

These estimates are based partly on assumptions (for example, on how effective the vaccine would be). Vaccines for pregnant women to prevent transmission of GBS infections are in development but not yet available.

In the UK (as well as other developed nations) the risk of GBS causing pregnancy complications or affecting the newborn is low. Read more advice about the risks of GBS in pregnancy.

Where did the story come from?

The study was carried out by researchers from the London School of Hygiene & Tropical Medicine, King's College London, the University of Bristol and other institutions in the UK, Africa, Europe and the US. The study was funded by the Bill & Melinda Gates Foundation.

The individual researchers received funding from various foundations, such as the Wellcome Trust, for their research. Some of them have done consultancy work for, or had research funded by pharmaceutical companies. The study was published in the peer-reviewed medical journal Clinical Infectious Diseases as part of a special supplement on GBS. It is freely available to access online.

The Guardian's coverage of this topic was generally balanced.

Bazian Ltd, which provides analysis for Behind the Headlines, has carried out work relating to screening for GBS in pregnancy for the UK National Screening Committee.

What kind of research was this?

This was a modelling study that aimed to give a worldwide snapshot of the rates and impact of group B streptococcus (GBS) infection in pregnant women and their infants in 2015.

GBS is a common bacterium that is usually harmlessly carried in the digestive system or vagina of around 1 in 5 women. Most pregnant women who carry GBS bacteria have healthy babies. However, very rarely it can cause problems during pregnancy, such as miscarriage and going into labour early.

There is also a small risk of the infection being passed on to the baby during delivery, which can sometimes cause a potentially serious infection in the newborn. This infection can be life threatening, or lead to developmental problems in the child.

Currently, the main way of preventing GBS infection in the newborn is by giving antibiotics during labour to pregnant women who are at higher risk. Different countries use different methods to identify which women are at higher risk. However, giving antibiotics in labour would not prevent miscarriages or premature births caused by GBS, or infections that arise more than seven days after birth. No vaccine is currently available, but if one were, it might be able to prevent more deaths than using antibiotics alone.

This study aimed to gain a better understanding of how many mothers and babies are affected by GBS, and to estimate the possible impact a vaccine could have.

What did the research involve?

The first part of the study aimed to estimate the number of pregnant women and newborns with GBS infection in 2015 and the associated disability worldwide.

In brief, the researchers used computer modelling to calculate their estimates, based on data available in the literature and various assumptions when the exact data they needed was not available. They used systematic searches to identify relevant literature.

The researchers used modelling approaches to estimate, country by country as well as globally, the:

numbers of women carrying GBS in their digestive system or vagina
rates of early-onset GBS infection (starting in the first week of life) and late-onset GBS infection (starting after the first week) in newborns
number of infants with meningitis, brain damage and severe developmental impairment resulting from GBS
premature birth rates resulting from GBS
infant fatality and stillbirth rates resulting from GBS
types of GBS bacterium associated with maternal and infant infection

The researchers then looked at the influence of various factors, such as:

the country or region
whether the area had good healthcare with skilled birth attendants
if mothers were given preventative antibiotics at the time of birth

What were the basic results?

Estimated exposure and infection rates

The researchers found that about 15% of all infants born worldwide in 2015 had been exposed to GBS at the time of delivery: 21 million of 140 million live births.

There were about 319,000 cases of invasive GBS infection worldwide, about two-thirds of which (205,000 cases) were early-onset infection. Asia had the highest rate of early-onset infection, while Africa had high rates of late-onset infection. Half of all cases occurred in Africa.

There were 90,000 deaths in infants aged up to three months due to GBS infection. Just under two thirds (60%) of these deaths occurred in Africa and 34% in Asia. Most deaths occurred in developing countries with poor access to healthcare. Fewer than 1% of infant deaths related to GBS occurred in developed countries like the UK. Similarly, developmental impairment following meningitis infection was far less common in developed countries.

GBS was also estimated to be responsible for up to 3.5 million preterm births and 57,000 stillbirths worldwide in 2015.

Potential effects of antibiotics and vaccines

The researchers estimated that giving antibiotics during labour had prevented 29,000 cases of early-onset infant infection and 3,000 infant deaths worldwide in 2015. Their model suggested that if all high-risk women were identified worldwide and antibiotics given during labour to at least half of these women, this could prevent about a third of deaths (27,000) and about 40% (83,000) of cases of early-onset infection.

Meanwhile it was estimated that if an effective GBS vaccine were available that could prevent 80% of cases and be given to about half of women, this could prevent about 40% of infant and maternal GBS cases (127,000) and infant deaths (37,000), as well as 23,000 stillbirths. Ensuring the vaccine was given to 90% of women could prevent 70%.

The most common GBS strain is type III. It is estimated that a vaccine covering the five most common strains (Ia, Ib, II, III and V) would cover 96% of the known GBS strains growing in the digestive and vaginal tracts worldwide.

How did the researchers interpret the results?

The researchers conclude that their estimates suggest GBS plays a major role in causing childbirth complications.

They suggest that: "An effective GBS vaccine could reduce disease in the mother, the fetus, and the infant."

Conclusion

This study provides valuable estimates of the global impact of group B streptococcus infection among pregnant women and newborns.

It produces some useful observations. It shows that GBS is responsible for many complications and deaths worldwide, with most of these complications occurring in developing regions such as Africa. In these regions it is likely to be harder for mothers and babies to access effective healthcare.

It also gives some reassurance that although 15% of newborns are estimated to be exposed to GBS during delivery, only about 1.5% of these exposed newborns develop infection.

It is worth bearing in mind that these figures are estimates, and that all models have to make some assumptions, which may or may not turn out to be correct. The researchers used stringent methods to find relevant data in the literature. However, some data may not be available, or may not give reliable figures on the prevalence of maternal or infant infection and associated illness for various reasons. For example, not all cases might be detected or some cases may be recorded inaccurately, particularly in developing countries. Similarly, the modelling techniques used to estimate the potential impact of maternal antibiotics or vaccination may not be accurate or take account of all potential influencing factors.

In the UK it is recommended that pregnant women identified to be at risk of GBS infection are offered preventative antibiotics at the time of delivery. They may be identified on the basis of risk factors such as:

past pregnancy where the baby was affected by GBS infection
GBS detected in a urine sample or in the vagina or digestive tract during their pregnancy
going into labour early
showing signs of infection during labour (such as fever)

The current research has estimated the global impact of GBS infection, and suggested that improving adherence to current guidance around preventing GBS could reduce the number of cases.

An anti-GBS vaccine for women is reported to be in development, and once it is ready it will need to be tested to assess its efficacy and safety. As the researchers suggest, it could potentially have advantages over using antibiotics alone during labour. The current research may spur on these efforts.