A live, genetically modified flu virus can infect animals and trigger a strong immune response, but cannot multiply in its host's cells. Such modified viruses could one day be used to improve on current vaccines (pictured).
Vaccines made of live viruses elicit stronger protective immune responses than inactivated vaccines, but, because they can replicate, have the potential to cause disease. To overcome this, Demin Zhou and his colleagues at Peking University in Beijing genetically altered the influenza A virus so that it could be produced efficiently by special transgenic cells, but could not replicate in normal cells or in infected animals. When compared with a commercially available inactivated flu vaccine, the modified virus stimulated stronger immune reactions in mice, ferrets and guinea pigs. Mice given the new vaccine and then infected with the unmodified flu virus survived, whereas all unvaccinated mice died.