The drug has been losing strength for the multiple genetic mutations introduced accidentally. A new study conducted by researchers at the Pasteur Institute in Paris claims that the newer vaccines to combat tuberculosis worldwide are less effective than previous versions.The drug has been losing strength for the multiple genetic mutations in strains of bacillus Calmette-Guerin (BCG) introduced by error in the cultivation of the microbe for decades, according to these scientists. They also noted that the old and new vaccines should be tested again to determine which are most effective. According to the authors of this study, reported in the journal Proceedings of the National Academy of Sciences “,” the first BCG vaccine may provide better protection against tuberculosis, a possibility which should be confirmed with a formal evaluation in clinical trials. The bacillus Calmette-Guerin comes from “Mycobacterium bovis, the microbe that causes tuberculosis in cattle. Although it is effective in preventing TB in children, in the case of adults the results are less clear. After analyzing the genetic sequence of several strains of BCG, scientists have found changes over time.Thus, a vaccine strain called BCG Japan, developed before 1925, it generated a better immune response than other modern strains such as BCG Danish, BCG Glaxo and BCG Pasteur.