Chinese scientists have developed a live human bird flu vaccine after more than three years of research on animals, a chief researcher said Friday.

Tests of the cold-adapted, live attenuated H5N1 vaccine in mice and nonhuman primates showed that the vaccine provided complete protection in the animals against homologous and heterologous H5N1 virus challenge, said Chen Hualan, director of China's National Avian Influenza Reference Laboratory, who is in charge of the research.

"Our study represents a major advance in vaccine development for H5N1 pandemic influenza and we are very confident about its prospect," said Chen.

Chen said the new type of vaccine "has many revolutionary improvements" in terms of its protective efficacy, production technique, and usage.

Vaccinated rhesus macaques remained healthy after they were injected with H5N1 virus as the vaccine stops the replication of the virus. But those infected animals without vaccination showed symptoms of fever, pneumonia and inappetence, similar to human infections.

Chen's team started the research and experiments in 2005, after a domestic epidemic that caused huge losses for poultry breeders.

The research results of the new vaccine was published on Friday's edition of the PLoS Pathogens, an international journal published by the Public Library of Science (PLoS).

H5N1 influenza viruses have infected 421 people, including 257 killed, in 15 countries with a high fatality of 61 percent.

Therefore, the development of effective vaccines is a priority for H5N1 pandemic preparedness, according to the article.

Human vaccines had been generated in some regions in the world. China's food and drug regulators authorized a Beijing-based pharmaceutical firm to begin commercial production of a human bird flu vaccine in April last year.

A high dosage of adjuvants improve the immunogenicity of H5N1 inactivated vaccines, but limited production capacity for conventional inactivated influenza virus vaccines could severely hinder the ability to control the spread of H5N1 influenza through vaccination, Friday's article pointed out.

The vaccine becomes effective by just spraying it into people's noses.

Production of the live vaccines requires much less chicken embryos than the traditional inactivated vaccines, which allows large-scale production and massive storage, Chen said.

He said China's National Avian Influenza Reference Laboratory is soliciting support from relative authorities and is looking forward to production after clinical appraisal.

Japanese influenza expert Yoshihiro Kawaoka and immunology expert Xiaoning Xu have contributed to the research during the final stage.

(Xinhua News Agency May 2, 2009)