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In a recent phase 2 trial, an experimental tuberculosis vaccine, H4: IC31, and Bacillus Calmette-Guérin vaccine, or BCG, were both ineffective against the initial infection Mycobacterium [19659002] tuberculosis .
However, revaccination with BCG in adolescents who were first vaccinated during infancy was badociated with a significant reduction in mortality M. tuberculous infection according to the researchers.
"The efficacy of the primary BCG vaccine against the disease is highly variable in different populations; it is thought that the efficacy is greatest in people without previous exposure to mycobacteria and may last 10 years." Elisa Nemes PhD, Principal Investigator at the South African Tuberculosis Vaccine Initiative of the University of Cape Town, and his colleagues wrote in New England Journal of Medicine . "Our findings suggest that BCG revaccination of [ M. For the trial, Nemes and his colleagues randomly badigned 990 South African adolescents in a ratio of 1: 1: 1 to receive H4 : IC31 (Aeras, Sanofi Pasteur), BCG or placebo revaccination All participants underwent neonatal BCG vaccination and had a negative M. tuberculosis and HIV score at the time of treatment.
The purpose of the test was to test the efficacy of the vaccine based on the prevalence of the asymptomatic disease M. tubercular infection This is unique for vaccine trials antituberculous drugs, which generally rely on the clinical effectiveness of the onset of tuberculosis, said one of the researchers.
There are barriers to screening for asymptomatic infections, reported Nemes and colleagues, although the acquisition, the persistence and the utorisation of M. tuberculosis infection can be important indicators of the effectiveness of the vaccine, they can not be measured directly with the available tests. The test used in the current study – QuantiFERON-TB Gold In-tube (QFT, Qiagen) – has no optimal threshold for infection, according to the researchers. However, badessing the asymptomatic infection instead of the occurrence of a disease can speed up the delay before obtaining clinical results.
"Although the clinical significance of the QFT reversion remains to be established, we propose that sustained QFT conversion is more likely to represent the M sustained tuberculosis and a higher risk of progression. to disease as transient QFT conversion, "writes Nemes and colleagues.
After a 2-year follow-up period, QFT conversion occurred in 14.3% of participants who received H4 : IC31, 13.1% of those receiving BCG and 15.8% who received placebo.) A sustained conversion was reported in 8.1% of participants who received H4: IC31, 6.7% of those who received BCG and 11.6% given a placebo.
None of the two vaccines reached the primary endpoint of prevention of initial conversion of QFT.The effectiveness of the vaccine against initial conversion was 9.4% for the H4: IC31 vaccine and 20.1% for the BCG vaccine. x vaccines reduced sustained conversion, only BCG had a significant impact, preventing 45.4% of conversions (95% CI, 6.4-68.1, P = 0.03) . H4: IC31 was 30.5% effective against sustained conversion (95% CI, -15.8-58.3 P = 0.16) and did not differ significantly from placebo, according to Nemes and colleagues.
Adverse events occurred in 550 participants. Most were reported among those who received BCG revaccination; however, they were mainly of mild to moderate severity.
Because there is no definitive test for Nemes and his colleagues said that the clinical implications of the results are limited. However, their study illustrates the value of measuring sustained QFT conversion rather than initial QFT reversion alone by using M. tuberculosis as an indicator of vaccine efficacy.
"Our results raise important questions regarding the prevention of M. tuberculosis for the control of tuberculosis and provide a promising signal for the BCG vaccine," concluded the researchers. . "These encouraging results prompt a reevaluation of the use of BCG revaccination of populations free of M. tuberculosis infection for the prevention of disease." – by Stephanie Viguers
Disclosure s : Nemes does not provide any relevant financial information. Please consult the study for the relevant financial disclosures of all other authors.
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