Older Vaccines May Protect Better than New

Older versions of vaccines used worldwide against tuberculosis could be more effective than the latest immunizers, according to a new study.

Researchers at the Pasteur Institute in Paris found multiple genetic mutations in strains of bacillus Calmette-Guerin (BCG), accidentally introduced as the microbe was cultured over decades, reduced the efficacy of the vaccine.

They concluded that old and new vaccines should be retested in clinical trials to determine which are the most effective.

“Early BCG vaccines may confer better protection against tuberculosis, a possibility that would benefit from formal evaluation in clinical trials,” researchers said in the study.

The study appeared in the current issue of the Proceedings of the National Academy of Sciences journal.

BCG is a crippled derivative of mycobacterium bovis, the microbe that causes tuberculosis in cattle, and is particularly effective in preventing tuberculosis in children, but results are variable in adults.

Researchers looked at the entire genetic sequence of several BCG strains and found changes over time.

By studying immune responses in infants, one vaccine strain called BCG Japan, an early strain developed prior to 1925, triggered a more powerful immune reaction than the vaccine strains BCG Danish, BCG Glaxo and BCG Pasteur, which represented 66 percent of the vaccine doses administered in 1996.

Tuberculosis is a common and deadly infectious disease caused by a pathogen, usually attacking the lungs.

Symptoms include a productive, prolonged cough, chest pain, and coughing up blood.

If left untreated, active TB disease kills more than half of its victims.

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