New Vaccine Reduces TB Incidence by 37% Among HIV-Positive People, Study Says
A new tuberculosis vaccine reduced the incidence of the disease by 37% among HIV-positive people during a clinical trial in Tanzania, according to a study presented by lead researcher Ford von Reyn at the 39th Union World Conference on Lung Health in Paris, This Day reports.
For the study, researchers from Dartmouth Medical School and Dar es Salaam's Muhimbili University of Health and Allied Sciences examined the efficacy of a vaccine created from a whole inactivated mycobacterium called M. vaccae, which previously had been tested for safety and immunogenicity during human studies conducted in Europe, North America and Africa. Beginning in 2001, the researchers recruited 2,000 HIV-positive people with an average CD4+ T cell count of 400 to participate in the study. All of the study participants previously received the Bacille-Calmette Guerin TB vaccine, and 70% of the study participants were women. The investigators randomly assigned the participants to receive five immunizations with the active vaccine or a placebo over a period of 12 months. Eighty-five percent of the participants received all doses of the vaccine.
During a three-year follow-up period, the researchers observed 207 cases of active TB and 20 cases of disseminated TB, which occurs when the disease spreads from the lungs to other areas of the body. The researchers also identified 33 cases of confirmed TB among the group receiving the vaccine and 52 cases of confirmed TB among the placebo group, indicating a vaccine efficacy of 37%. Von Reyn said that if 50% of HIV-positive people in Tanzania received the vaccine, TB incidence in the country could decline by about 3,300 new cases annually.
According to von Reyn, the low incidence of disseminated TB can be attributed to the aggressive efforts of trial physicians to diagnose TB before it spread from the lungs. A lack of trial follow-up also could account for the low incidence, as 16% of participants failed to continue the trial, possibly because of sickness. Although the study found no significant reduction in the rates of probable TB, the vaccine appeared to maintain its protective effects for one year when the researchers plotted the event rate in a Kaplan-Meier graph, This Day reports.
According to the study investigators, reducing the TB incidence by 37% demonstrates that the new vaccine provides significant protection against TB, because "anything more than 20% is very favorable in the context of a very common complication of AIDS," von Reyn said. He added that Tanzania's Ministry of Health and Social Welfare is interested in implementing a vaccination program, which would require licensing the vaccine and identifying a manufacturer capable of producing sufficient amounts for large-scale immunizations. According to von Reyn, a remaining challenge for the vaccine will be to examine its effects among HIV-positive people with CD4 counts fewer than 200 (This Day, 10/22).
Kaisernetwork.org is the official webcaster of the Union TB conference. Webcasts of select sessions, interviews and other resources are available online.