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Medicine

Researchers upbeat despite failed TB trial

The long-awaited results from trials for a new tuberculosis vaccine have shown no protection against the disease in infants. But the scientists say the results will stimulate new research.

Petri Dish
Photo: Hubert Link +++(c) dpa - Report+++

Petrischale Bakterien

There is good news. And there is bad news.

Here is the good news first: the vaccine - known as MVA85A - is safe, shows no dangerous side effects and induces modest immune responses.

But the bad news is it offers no extra protection against tuberculosis (TB) - at least not in infants, on whom the vaccine was tested in South Africa.

Helen McShane at Oxford University co-developed the vaccine. She says that while the results are disappointing, there is a lot that can to be learned from them.

"We can understand more about the type and level of immune response the body needs to generate against TB," says McShane. "That will boost future efforts to develop an effective TB vaccine."

There are about a dozen more vaccine candidates being tested in clinical trials.

"Historical step"

"The results are not what we wanted to see but I wouldn't say the trial was unsuccessful," Willem Hanekom, director of the TB vaccine research group in South Africa, told DW. "We thought we had a strategy that might work but in the end it did not. Now we have to find out why."

It may be necessary to use a higher dose or even multiple doses - or perhaps the vaccine should be administered by inhalation, not by injection, Hanekom speculates.

Mycobacterium tuberculosis Photo: Robert-Koch-Institut/Gudrun Holland

Tuberculosis is caused by the bacterium Mycobacterium tuberculosis

Christian Lienhardt from the World Health Organization (WHO) also prefers to consider the outcome of the trial positively.

"It is a historical step," says Lienhardt. Even though the vaccine failed to protect against the disease, there was a modest immune response, insists Lienhardt. "So there was something. We now have to find out more about it."

Replacement for old vaccine

McShane says that everyone working in the field of TB vaccines research will now benefit from the data from these clinical trials.

"It is only through the difficult business of evaluating candidate vaccines in humans that we will really move forward in understanding how we might improve on BCG," says McShane.

BCG is the established tuberculosis vaccine Bacillus Calmette-Guérin. It can protect babies against severe outbreaks of TB, with a high rate of success.

"But it offers less or even no protection at all for adults," explains Ernst Molitor, senior physician at the University of Bonn's Institute of Medical Microbiology, Immunology and Parasitology.

Adult patients often develop a pulmonary TB.

Petri Dish with bacteria culture
Photo: Jan-Peter Kasper/FSU

The current TB vaccine BCG consists of live bovine tuberculosis bacteria

No boosting effect

MVA85A was designed to boost immune responses already induced by the BCG vaccine.

The researchers injected almost 2,800 babies in South Africa with MVA85A. All children had received a prior BCG vaccination.

During the following three years, 39 children in the placebo group developed TB, compared to 32 children in the MVA85A group.

Even though these results show a vaccine efficacy of 17 percent, the difference is not considered statistically significant - it could be down to mere chance.

A major killer

Almost 9 million people fall ill with TB every year. And more than a million die.

TB ranks as the second leading cause of death from an infectious disease worldwide - second after HIV.

"[We really need] a more efficient vaccine against TB," says Ernst Molitor. "Especially since drug-resistant TB bacteria are on the rise."

It is easier said than done. When the body is infected with a disease, and the disease is eliminated, the body often develops an immunological memory, which allows it to mount faster and stronger responses in future. But this is not the case with TB.

"Even if you get tuberculosis and survive it, you don't get life-long immunity," Molitor says.

A doctor examines chest X-rays Photo: ddp images/AP Photo/Karin Schermbrucker

Tuberculosis most often affects the lungs

More candidates in the running

The BCG vaccine consists of weakened live bovine tuberculosis bacteria, which are no more dangerous to human health - unless a person has an immune deficiency.

MVA85A derives from the cowpox virus MVA (Modified Vaccinia Ankara). It produces a protein which is typical for the tuberculosis bacteria. And because of this, it was supposed to provoke immune responses.

It failed. But there are more candidates in the running.

Eleven more vaccine candidates are being tested at different stages of clinical trials worldwide.

Some of them are genetically improved versions of BCG, which could replace the current but inefficient vaccine. It is hoped that other candidates will supplement BCG - just like MVA85A.

"They all use different tactics," says Christian Lienhardt at WHO. But at the moment it is impossible to say which one is the most promising. "We'll have to wait and see."

DW.DE

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