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A Century-Old Vaccine Fails to Protect Against Covid
Early in the pandemic, scientists began testing an old TB vaccine against the coronavirus. But the trial enrolled fewer participants than expected as new Covid vaccines were introduced, and no discernible effect was found.
An old tuberculosis vaccine known to bolster the immune system did not prevent Covid infections among health care workers, scientists reported on Thursday.
But the trial was shorter and smaller than originally designed, and the investigators said that the results did not rule out other potential benefits associated with the vaccine, known as B.C.G. for bacille Calmette-Guerin.
The study, published in The New England Journal of Medicine, was the largest clinical trial of the vaccine’s potential to protect against Covid infections. B.C.G. was developed in the early 1900s to combat TB, but has since also been shown to confer protection against other illnesses, including respiratory diseases.
The trial of health care workers began in March 2020, during the early days of the pandemic, when no effective treatments for Covid were available and a new vaccine against the highly infectious disease seemed to be a remote fantasy. The hope was that the old vaccine might be repurposed to save lives.
Six months after vaccination with B.C.G., however, there were no significant differences between the two groups of health care workers: While 14.7 percent of those inoculated with B.C.G. developed symptomatic Covid infections, 12.3 percent of those who received saline placebo shots got sick.
Five participants in each group were hospitalized, and one participant who got the placebo died. The differences were not statistically significant.
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