New Strides Towards a GBS Vaccine

At birth infants are especially susceptible to bacterial infections, particularly Group B streptococcus or GBS. For this reason, OB/GYN's routinely test all pregnant women to see if they are carriers of GBS. 25 to 30% of pregnant women carry GBS, and all of them receive antibiotics during labor to help prevent transmission to the infant. If an infant becomes infected with GBS, the effects can be devastating, even causing death or permanent disability.

Giving women antibiotics for GBS during labor and delivery has led to a lower incidence of infants infected with GBS immediately after birth. However, we have yet to lower the risk for premature babies or lower the rate of GBS disease that occurs after the immediate postpartum period.

For this reason, medical professionals have long hoped for a vaccine against GBS that could help with these unsolved issues and perhaps even eliminate the need for antibiotics during labor, which can lead to antibiotic resistance and allergic reactions. Passive immunity is immunity that is acquired by the growing fetus while still in the womb. A mother’s immune cells, known as anti-bodies, can pass from the mother’s bloodstream through the placenta to the fetus. These antibodies help protect the baby in the first few weeks or months of life when the baby’s immune system has not yet developed. The most antibodies are transferred from mother to fetus in the third trimester pregnancy. For this reason we give mothers the tetanus-diphtheria-acellular pertussis vaccine or Tdap vaccine in the third trimester. We also give mothers the flu vaccine to help protect both the mother and the infant from the flu. 

In the February 2016 issue of the Green Journal, Dr. Donders and his group from Femicare Clinical Research for Women and the Tienen University Hospital in Antwerp present some very exciting research on a vaccine under development for GBS. They conducted the randomized clinical trial at two hospitals in Belgium and three hospitals in Canada from 2011 to 2013. Fifty-one women received the investigational GBS vaccine, and 35 women received a placebo salt water injection in their arm.

The authors measured everything from side effects after the shot to the mother’s immune response at multiple time points after the shot. They also measured the infants’ immune response at birth and three months after birth. It’s important to remember that the number of subjects included was small, so the study is more of a proof of concept than definitive evidence of the vaccine safety and efficacy.

Women had similar injection site and system-wide reactions with the real vaccine and the placebo shot. Both groups most commonly reported pain, headache, and fatigue immediately after the shot. Mothers showed an increase in immunity of 20 to 30 times after the vaccine. Women who had higher levels of baseline immunity had a better response to the vaccine. But, even women with low baseline immunity had a better response than the placebo group. Women who received the placebo had no change in their antibody concentrations.

Infants of vaccinated mothers also had higher immunity levels, about 5 to 8 fold more than infants whose mothers received the placebo shot. Infants received about 75% of their mothers’ immunity levels. Infants retained about three-quarters of this immunity at 3 months of age. With regard to the initial safety profile for infants, there weren’t any differences in birth weight or gestational age at birth between the two groups of infants.

Remember that Tdap vaccine we also give mothers and infants? Will this new GBS vaccine interfere with the Tdap vaccine? The authors also tested infants’ immune response to the Tdap vaccine, given after birth. The GBS vaccine did not interefere with the infants’ immune response to the Tdap vaccine.

This exciting study provides good news for a vaccine to protect infants from GBS. It will be exciting to see how the next phase of research develops in making this vaccine a reality for routine clinical practice.