Centuries-old TB vaccine does not protect against Covid
An old tuberculosis vaccine known to boost the immune system did not prevent Covid infections among healthcare workers, scientists reported Thursday.
But the study was shorter and smaller than originally planned, and investigators said the results don’t rule out other potential benefits associated with the vaccine, known as BCG 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 infection. BCG was developed to fight TB in the early 1900s, but has since been shown to protect against other diseases as well, including respiratory diseases.
The trial of healthcare workers began in March 2020, in the early days of the pandemic, when no effective treatments for Covid were available and a new vaccine for the highly contagious disease seemed a distant fantasy. The hope was that the old vaccine could be reused to save lives.
However, six months after vaccination with BCG, there were no significant differences between the two groups of health workers: while 14.7 percent of those vaccinated with BCG developed symptomatic Covid infections, 12.3 percent of those who received saline placebo shots developed the disease.
Five participants in each group were hospitalized, and one participant who received the placebo died. The differences were not statistically significant.
The remarkably rapid development of mRNA vaccines made it impossible to complete the BCG trial as planned, as healthcare workers were put first to getting the newly available mRNA vaccines.
The aim of the BCG study was to follow 10,000 participants from five countries – Australia, the Netherlands, Spain, the UK and Brazil – for 12 months, but the new paper reports just 4,000 adults followed for six months.
The mRNA vaccines are “an absolute marvel of modern science,” said Dr. Nigel Curtis, the study’s lead researcher, who is a professor of pediatric infectious diseases at the University of Melbourne in Australia. “But from a process perspective, it was pretty disastrous.”
An even larger study would have been needed to determine whether the vaccine not only protects against infection but also against hospitalizations and deaths from Covid.
The vaccine is still widely used in developing countries, where many babies die before their first birthday. Scientists have found that BCG vaccination reduces infant mortality. In addition to protecting babies from tuberculosis, the vaccine appears to train the immune system to respond to other pathogens, reducing rates of respiratory and other illnesses.
“The conclusion of our study – that BCG does not protect healthcare workers from mild or moderate Covid – is true,” said Dr. Curtis.
But it could still show promise, he added: “This doesn’t tell us anything about the ability to protect people in other age groups from infection.” BCG is still a very important concept in infants.”
Additional analysis of data collected from vaccinated healthcare workers continues. The vaccine’s effect may vary depending on the virus or bacteria it’s targeting, said Dr. Curtis.
The BCG vaccine contains live modified bacteria that have been grown in laboratories around the world for decades, introducing mutations that have resulted in a number of strains. Different BCG strains and different inoculation schedules may account for conflicting results in other studies, some experts say.
One of the most successful to date was a small study of adults with type 1 diabetes who received multiple BCG shots before the pandemic to improve their blood sugar levels and reduce infections.
This study found that those who received BCG had far fewer Covid infections than participants who received placebo shots.