MVA85A does not protect against pulmonary tuberculosis

The most promising vaccine to replace the world's 91-year-old tuberculosis jab does not protect against the disease, according to results released Monday of large-scale trials conducted among infants in South Africa.

Doctors have had high hopes for the formula, known as MVA85A, as the existing Bacille-Calmette-Guerin (BCG) vaccine does not protect against pulmonary TB, the most common form of the disease among adults and adolescents.

MVA85A was found to be safe and had no side effects, but “did not provide statistically significant protection” against the TB microbe, the researchers announced.

What got them excited?

The trial was a so-called Phase IIb, comprising the intermediate step between the second and final phases of the long process by which drugs are vetted for safety and efficacy.

MVA85A is the first TB vaccine candidate to reach this stage since BCG, which was licensed for humans in 1921.

The trial, launched in 2009, saw the drug tested on 2,800 infants in South Africa's Western Cape province who did not have TB or the AIDS virus.

The vaccine efficacy was observed to be 17.3 per cent. The results are disappointing but should also provide vital insights, said senior researcher Helen McShane.

“The results from this study should let us know far more about the type and level of immune response required, and that will boost future efforts to develop an effective TB vaccine,” she said.

“The difficulty of this task is one reason why there has not been a new TB vaccine since BCG was developed more than 90 years ago, but one is still urgently needed and I’m not about to give up now.”

More than a dozen TB vaccines are under trial around the world, a figure that has risen sharply over the past decade.

Not the end of the road

In a commentary also published by The Lancet, TB experts said the verdict for MVA85A was not “terminal”.

It could show higher protection in other TB settings, they said.

MVA85A is also being tested in a Phase IIb study among people with HIV in Senegal and South Africa, a Phase IIa study in infants born to HIV-positive mothers in South Africa, and in Phase I studies in Britain.

Also unexplored is whether MVA85, working as booster to the BCG, can protect adolescents and adults against pulmonary TB even though it cannot do this for infants, the pair said.


Quick facts

  • TB is an infection caused by Mycobacterium tuberculosis and is one of the world's deadliest diseases.

  • In most countries children are vaccinated with BCG, but this does not protect adults from pulmonary TB, the most common and infectious form of the disease, and has limited efficacy in children.

  • MVA85A is the first TB vaccine candidate to reach Phase IIb in the trials since BCG, which was licensed for humans in 1921. Unfortunately it did not pass.