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TB vaccine candidate to enter final trial, raising hopes of saving millions

Efforts to end the tuberculosis pandemic may get a long-awaited boost after a promising vaccine candidate secured funding for its final phase of clinical trials.

The Bill and Melinda Gates Foundation and Wellcome announced Wednesday they would put about $550 million into Phase III trials for a tuberculosis vaccine originally developed by the drug company GSK. The shot, called M72, has been on hold since 2019, when GSK abandoned it because it lacked commercial potential.

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If the next phase of trials is successful and regulators approve, M72 would be the first new vaccine in a century to target a disease that killed 1.6 million people in 2021.

Tuberculosis infected more than 10 million people in 2021, the vast majority of them in low- and middle-income countries, the World Health Organization says. Among infectious diseases, only covid-19 was deadlier.

TB is more commonly treated using drug therapies. A vaccine for TB works mostly in infants and children, who make up a tenth of the infected population.

Proof-of-concept trials for M72 suggested it could prevent pulmonary disease in 54 percent of TB-infected adults. The WHO benchmark for TB vaccines is 50 percent efficacy in adults.

"Scientifically, it's huge," said Eric Rubin, a researcher at the Harvard T.H. Chan School of Public Health and editor of the New England Journal of Medicine, whose lab studies the bacterium that causes TB. "If you were able to drive down the rate of TB by half, that would save a really substantial number of lives in the world."

It has taken 100 years for a new TB vaccine to advance. The existing jab, known as the BCG vaccine, first rolled out in 1921 and is only moderately effective, even in children.

Drug-resistant strains of the disease multiply each year, said Rubin, also a professor at the Harvard School of Public Health. Eradicating the disease is also complicated because most treatment programs rely on patients to seek help and return for treatment over several months.

The delay between M72's trial phases highlights persistent issues with inequity in treating infectious disease, said immunologist Thomas Scriba, the deputy director of the South African Tuberculosis Vaccine Initiative (SATVI), which is helping organize the Phase III study. SATVI was also involved in the vaccine's 2019 trial.

GSK licensed its experimental TB vaccine to the Gates Medical Research Institute in 2020, after deciding not to fund the Phase III trials. The vaccine shares a key component with another GSK offering, a shingles shot that has generated billions for the company. Many shingles patients live in higher-income countries such as the United States, where most health insurers can pay for it.

"With covid, we saw vaccines and even treatments that are still not available for us in the Global South," Scriba said. "Should this vaccine show efficacy and be licensed, we must absolutely make sure it's going to be available to those who need it."

The M72 vaccine isn't the only promising candidate in development to treat TB. Afrigen, a WHO-supported hub in South Africa, began work on its own vaccine last year using the mRNA technology that powered the most effective coronavirus shots. The Gates Medical Research Institute, which focuses primarily on diseases prevalent in lower-income countries, is also working on other TB vaccines and therapeutics.

M72 has outpaced more than a dozen other candidates. Researchers will enroll 26,000 people at trial sites across Africa and Southeast Asia beginning next year to test it among a large pool. Scriba said the trial's end date will depend on how long it takes for a sufficient number of participants to become infected. Only 39 people in the vaccine's Phase II trial became sick, a small sample size compared with what researchers will attempt.

The approval process and rollout may also present logistical and financial hurdles, meaning the trial funding is only one step toward another widely available TB vaccine. Such a shot would prevent 8.5 million deaths during the next 25 years, the WHO estimates.

If it proves effective and safe, M72 will probably not eradicate TB. Alexander Pym, the director of infectious disease at Wellcome, called it "a valuable addition to our tool kit" in a news release. New public health measures, therapeutics and diagnostics also form part of the WHO's strategy for reducing deaths from the disease 90 percent by 2030.

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