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Wednesday, December 7, 2022
CAPE TOWN, Aug 3 2009 (IPS) - For the first time in eighty years, a new Tuberculosis (TB) vaccine has entered the efficacy stage of a clinical trial. While the developers are optimistic about the outcome, lung health and TB experts are warning against being overly excited.
"The bacteria that causes TB is a tricky one, as people can get the disease more then once – which is different when one looks at conditions such as measles," said Anthony Harries, head of the research department of the International Union Against Tuberculosis and Lung Disease.
The organisation, with headquarters in Paris aims to bring expertise, solutions and support to address health challenges in low- and middle-income countries.
"This makes developing a vaccine that protects people for their entire lifetime much more difficult than vaccines against other once-off diseases," Harries said.
"From what I know, the developers have managed to take out and isolate the gene of the TB bacteria that stimulates an overall immune response," he added. "That is wonderful, but I think we should wait and see how the trial goes before we jump for joy."
The TB vaccine, which is being tested in Worcester, about an hour's drive from Cape Town, has been developed by the South African Tuberculosis Vaccine Initiative (SAATVI), with support of the Aeras Global TB Vaccine Foundation (AERAS); an organisation that is dedicated to HIV/TB research.
"We acknowledge that is it more difficult to develop a vaccine for TB compared to diseases like hepatitis, as one can get TB more then once," Sadoff told IPS.
"You therefore need to develop a drug that triggers a different reaction from the immune system. It seems we have managed this: we have determined that the drug works in Phase-IIb, now we need to find out about the required dosage."
The announcement of the new TB vaccine trial took place during the 5th International Aids Conference on HIV Pathogenesis, Treatment and Prevention which was held in Cape Town in July 2009.
Clinical trials, during which a potential drug is tested on humans, comprise of three stages or phases. Phase-I aims to see whether the drug is safe to use for people, and involves a small group of 20-50 volunteers.
Phase-II, which aims to determine whether the drug is working, involves several hundreds of volunteers, and is often divided in two sub stages. While Phase-IIa assesses how well the drug works, Phase-IIb focuses on how much of the product should be given to a patient to do the job.
The final and third phase of a trial is the definitive assessment of the potential new drug. Phase III involves a larger number of volunteers, sometimes several thousands, which is divided into two: one group receives the actual drug, the other is given a placebo drug.
It can take up to twenty years before a potential new drug is given the green light.
A drug that has successfully passed a Phase-II study does not necessarily make it all the way. In 2007, a Phase-III trial of a microbicide gel intended to prevent HIV infection in women was stopped after scientists found that the participants using the gel were experiencing higher rates of infection than the placebo group.
The development of the candidate TB vaccine started eight years ago, and will be tested in over 2,700 young children over the next few years.
"If everything goes according to plan, a vaccine will be available in 2016," Sadoff said.
One of the concerns that was raised during the conference by civil society among others , is whether people in developing countries – who bear the brunt of the disease – will be able to afford the vaccine.
"The price of the new vaccine will not change, and will be around eight to ten U.S. cents per dose," Sadoff explained. "This is comparable to the price of the current vaccine BCG."
The reason behind the development of a new TB vaccine is that the current Bacille Calmette-Guérin vaccine (BCG), developed in the 1920s, has proven ineffective in protecting adults from the TB bacterium.
"The BCG vaccine does protect children from developing serious forms of active TB, but only up until the age of 15. After that, a person is no longer protected," Harries said. "The problem with BCG is that you cannot give a second dose after the effect of the first one has worn off.
In Africa, it is mainly adults and young adults that develop TB, often due to also being infected with HIV. People living with HIV, due to their weakened immune systems, are more prone to the disease.
"It is estimated that people who are HIV positive have an annual 10 percent chance to develop TB," Harries explained. "People who are HIV negative, have a ten percent chance to develop TB in a lifetime.
According to the 2009 Global TB report by the World Health Organisation (WHO), 2007 saw 9.27 million new TB infections, and 1.7 million people worldwide – of whom 456.000 were infected with HIV – died of the disease.
In South Africa, one of the countries with the highest TB rates, of the 461,000 cases recorded in that year, 336,000 occurred among people living with HIV. Of the 112,000 people who died of TB, 94,000 were HIV positive.
Despite the enormity of the TB problem in Africa and developing countries elsewhere, scientists only started to look for a new vaccine some eight to nine years ago.
"After its introduction, BCG proved to effective in Europe, and prevalence declined rapidly," said Sadoff. "Therefore, people in the West considered the disease as beaten, and so no new vaccines were developed – despite the fact that TB came back with a vengeance in the developing world, especially among people living with HIV," he added.
"Essentially, it was recognised as a disease of the poor, so there was not a lot of interest. Things changed with the emergence of Multi-drug Resistant (MDR) and Extreme Drug Resistance (XDR) TB, which is considered a global threat that is not confined to Africa."
MDR-TB is resistant to the top two TB drugs, and XDR-TB to the vast majority of first- and second-line drugs. In 90% of the cases, XDR TB is fatal. Both forms of drug resistant TB can occur when TB patients do not adhere to their first-line drugs, which have to be taken for up to six months.
"To prevent people from dying as a result of TB – both the normal and the drug resistant varieties, we need this vaccine more then ever," Sadoff said. "And the chances are that we are very close to having one."
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