Vaccine against group B streptococcus

Sep 20 2005

Common bacteria that live harmlessly in the gastrointestinal tract and vagina of 25 percent of women can become lethal if a newborn gets exposed to them during birth.

Researchers are studying a vaccine that may one day eliminate that risk.

"If we could give a vaccine to prevent women from harboring group B streptococcus in the vagina, then babies are not going to get it," says Dr. Daron Ferris, family medicine physician at the Medical College of Georgia and a principal investigator on a National Institutes of Health study to explore that potential.

MCG as well as the University of Pittsburgh School of Medicine and Planned Parenthood of Houston and Southeast Texas, Inc., are enrolling a total of 600 healthy, non-pregnant women in the study.

Half the participants will get the new vaccine developed at Harvard University and the rest will receive a standard tetanus toxoid vaccine.

MCG's participation in the study is funded by an $800,000 NIH grant. Study sites include the Augusta campus as well as the University of Georgia's University Health Center in Athens and Georgia Southern University's clinics in Statesboro.

The group B strep vaccine is being compared with tetanus toxoid vaccine because the tetanus vaccine, long shown to be effective, is used as the delivery mechanism for group B vaccine, Dr. Ferris says. "It's piggy-backed onto the tetanus toxoid vaccine so the body makes antibodies to the tetanus and group B strep," he says.

Group B strep is the most common infectious cause of death in newborns, according to the Centers for Disease Control and Prevention. Problems typically surface within the first week of life when the immune system is immature and least able to fight off infection. Results may include overwhelming infection called septicemia, meningitis, pneumonia and long-term damage such as hearing loss, impaired vision and developmental problems.

The bacteria come and go in most women, infecting about 25 percent at any one time and – for unclear reasons – a higher percentage of black women and non-smokers, Dr. Ferris says. A Pittsburgh study of predictors of infection showed that sexual activity, in terms of frequency and/or number of partners, was highly associated with vaginal infection. Also, women with an imbalance in the protective bacteria that typically colonize the vagina are at increased risk.

The bacteria usually are harmless outside the bloodstream, so physicians usually don't screen for them or give antibiotics unless the woman is pregnant, Dr. Ferris says. In the late 1980s, physicians began testing for group B strep in the vagina and rectum at 35-37 weeks of gestation and administering an antibiotic to those who have it. The idea is that the bacteria is eliminated before the baby is born, Dr. Ferris says.

That approach has led to a dramatic decline in infection but has not eliminated it. Problems with current prevention protocols include premature delivery and a negative test at 35 weeks gestation with subsequent infection, Dr. Ferris says.

Still, rates of group B strep disease have dropped from a high of about 2 percent of 100 live births to about .5 percent, a rate that has held for several years, according to the CDC. The infection rate is about .8 percent for black newborns. Current estimates are that 1,720 newborns are infected annually and 70-90 babies die.

The SPIN study – Streptococcal Prevention In Non-Pregnant women – aims to reduce that number by helping women eliminate the bacteria before they become pregnant.

The study will compare group B infection rates in those receiving the new vaccine to those receiving only the tetanus vaccine, who will serve as controls for this study, Dr. Ferris says. Antibody levels to group B strep also will be measured over the 18-month study to see if they go up and stay elevated for an extended period. Phase one studies, conducted in pregnant women, showed the vaccine to be safe and resulted in high levels of antibodies in the mothers that were transferred to the fetus.

How long the protection lasts will help determine how the vaccine eventually is used, says Dr. Ferris. If it provides high levels of long-term protection, it could be recommended for all young women, which would help ensure protection in unplanned pregnancies. "If it's just say three to five years, we likely would need to target women who are interested in getting pregnant," he says.

The study is enrolling sexually active women age 18-40 using effective birth control. Partipants will be followed every two months for 18 months, receive a free physical and pelvic exam and be compensated for their participation.