TB trial raises vaccine hopes

RESULTS from the first Prevention of Infection TB trial has provided encouraging new evidence that TB vaccines could prevent sustained TB infections in high-risk adolescents.

Scientists from the SA Tuberculosis Vaccine Initiative (SATVI) and the Desmond Tutu HIV Foundation announced the results of an innovative clinical trial conducted in Worcester and Cape Town.

The trial tested the ability of Bacille CalmetteGuérin (BCG) and new vaccine candidate H4:IC31 to help prevent an initial or sustained TB infection. This was the first randomised, controlled, prospective trial conducted to study whether vaccination can prevent mycobacterium tuberculosis (MTB) infection in high-risk, healthy adolescents.

The BCG vaccine is nearly 100 years old. A single dose given at birth is moderately effective in preventing severe TB in infants and young children, but does not adequately protect teens and adults, who are most at risk for developing and spreading TB.

This study aimed to investigate if a second dose of BCG (revaccination) for adolescents might provide protection against MTB infection.

BCG showed a significant ability to help people control or clear a TB infection. BCG showed efficacy in preventing sustained TB infections – meaning participants who initially tested positive for TB infection were more likely to have cleared or controlled the infection within six months.

In the trial, revaccination with BCG significantly reduced sustained TB infections in adolescents, with a 45.4% vaccine efficacy.

The trend observed for H4:IC31 is the first time a subunit vaccine has shown any signal that it may be able to protect against TB infection or disease in humans.

SATVI director and principal investigator in this study Mark Hatherill said: “While neither vaccine proved to be statistically significant in preventing an initial TB infection, we are extremely encouraged by the efficacy findings against sustained TB infections. We believe the results… will provide significant scientific benefit to the field in understanding protection against TB infection.”

The study was approved by the Medicines Control Council of SA and the independent ethics committee at UCT.