Prevention
Currently, there are no vaccines for GBS. Prevention of GBS perinatal disease in high-risk pregnancies relies on:
1. Maternal GBS colonization screening and;
2. Intrapartum antibiotic prophylaxis (IAP)
Maternal GBS colonisation screening
Maternal screening for GBS colonisation is recommended for all pregnant women at 35- 37 weeks. In countries like the UK routine screening is performed for women and those with risk factors for GBS are given intrapartum antibiotic prophylaxis (IAP) at the time of birth.
GBS screening in most developing countries is however challenging as most women in these countries do not go for routine pregnancy check-ups.
Intrapartum antibiotic prophylaxis (IAP)
In the absence of a GBS vaccine, intrapartum antibiotic prophylaxis (IAP) is the currently recommended strategy for the prevention of early neonatal GBS infections. The administration of IAP is guided by the results of GBS screening or by risk-based protocols. The efficacy of IAP is therefore highly dependent on both the timely detection of GBS-colonised pregnant women and the antibiotic resistance profiles of the isolated bacterium.
Intrapartum antibiotic prophylaxis has been effective in the prevention of early-onset GBS disease (0-6 days) by 85 %, however, the use of IAP has no impact on late-onset of disease (GBS disease in infants 7- 89 days old), stillbirths or prematurity due to GBS. As such IAP has not been fully effective in reducing the overall GBS burden in infants.
Vaccine Development
Vaccines have been proposed as a long-term strategy against GBS disease as early as the 1970s in which it is envisaged that the immunisation of pregnant women would subsequently lead to the protection of infants. Infants would be protected through transplacental antibody transfer from their immunised mothers.
Several capsular Polysaccharide (CPS) conjugate vaccines and protein-based GBS vaccines are currently under development. Clinical trials for a hexavalent vaccine covering serotypes 1a,1b, ii and v has completed phase I and II and is expected to cover 98% of worldwide GBS cases.
Vaccine Development Challenges
The development of GBS vaccines have been severely impaired by multiple factors that include:
- The diversity and switching of the serogroups present a powerful immune evasion strategy.
- The development of vaccines is highly dependent on the presence of strong surveillance systems that would closely monitor the changing distribution of serotypes. These surveillance systems are at present limited in high burden and resource-limited contexts such as Africa and Asia.
- The low incidence rates of GBS disease makes vaccine efficacy studies more complex. As there is a good relationship between antibody response and protection against GBS infection, more rapid licensure could be achieved by measuring the antibody response (a serocorrelate of protection). Several studies to determine a serocorrelate of protection are currently underway in different global locations.
