New Delhi, Oct. 2: An Indian-made vaccine against typhoid has proved safe and effective in its first-ever human challenge trial and shown promise as a possible shield against typhoid fever in high-burden countries, researchers have said.

The trial, conducted by scientists at the University of Oxford in Britain and collaborating institutions, suggests that the vaccine made by the Hyderabad-based Bharat Biotech can prevent up to 87 per cent typhoid infections, the researchers said.

Their study, published in the journal Lancet, has been described as the first to suggest that immunisation with the vaccine could have a significant impact on the incidence of the disease in endemic areas.

Although typhoid can be treated with antibiotics, the Salmonella typhi bacteria -which spreads through contaminated water and food - has increasingly become resistant to common antibiotics. Scientists estimate that typhoid causes about 20 million infections and over 200,000 deaths worldwide every year.

In the trial, supported by the Bill and Melinda Gates Foundation, Oxford researcher Andrew Pollard and his colleagues administered the vaccine to adult volunteers who later "challenged" the infection by orally ingesting typhoid bacteria.

In conventional clinical trials of vaccines, scientists typically have to wait for a chance exposure to the infection - the vaccinated person needs to be bitten by a mosquito carrying an infectious microbe or needs to consume contaminated food or drink - to assess vaccine efficacy.

"In human trials, this chance element is eliminated; the volunteers are exposed to the infection," Krishna Ella, managing director of Bharat Biotech, told The Telegraph. "And the bacterial load is enormous, much higher than what might come from just natural exposure."

The company today said that all those who had received the vaccine showed an immune response and the vaccine prevented up to 87 per cent of typhoid infections.

The results of the trial are "highly significant" as those typhoid vaccines that are similar and currently available cannot be administered to children below two years, the company said. It added that its vaccine can be given to children below two and confers long-term immunity.

The vaccine is already licensed for commercial use in India, Nigeria and Nepal.