Researchers at St Jude Children's Research Hospital, Stanford University Medical Center, and MacroGenics have developed an antibody which is 100% protective against the deadly bird flu virus in two species of animal models.

A single, low dose of the new compound FcDART, for Fc (the type of fusion protein) Dual-Affinity ReTargeting molecule provided complete protection against lethal H5N1 viruses in laboratory models of influenza.

The dose can be given a day before infection or up to three days after.

"Laboratory models are rough approximations of what might happen in humans," said first author Mark Zanin, a post-doctoral fellow in Webby's lab at St Jude. "We did see complete protection against H5N1 in ferrets, which have long been used as a model for human flu, so we are confident in our results."

Antivirals are hampered by the capacity of viruses to rapidly mutate, which often results in resistance. Vaccines have to be designed for each flu and take months after a pandemic.

Antibodies work by targeting antigens on viruses as specifically as keys to locks, thus disabling them. Mutations can render antibodies ineffective. But the team devised a technique that makes it difficult for resistance.

"Our solution was to make a 'dual-specific' antibody by combining two different antibodies that attach strongly to H5N1 viruses into a single antibody-like molecule," said Richard Webby, PhD, a Member in the Infectious Diseases Department at St Jude Children's Research Hospital, Memphis, TN, and Director of the World Health Organization (WHO) Collaborating Center for Studies on the Ecology of Influenza Viruses in Lower Animals and Birds.

The research is published in the Journal of Virology, a publication of the American Society for Microbiology.

Since 2003, the H5N1 influenza virus, more commonly known as bird flu, has been responsible for the deaths of millions of chickens and ducks and has infected more than 650 people, leading to a 60% mortality rate for the latter.

Luckily, this virus has yet to achieve human-to-human transmission, but a small number of mutations could change that, resulting in a pandemic.

Outbreaks in Asia

The highly pathogenic H5N1 avian influenza virus, which has been causing poultry outbreaks in Asia almost continuously since 2003 and is now endemic in several countries, remains the animal influenza virus of greatest concern for human health.

The WHO recently voiced concern over avian influenza noting that the diversity and geographical distribution of influenza viruses currently circulating in wild and domestic birds are unprecedented.

"The world needs to be concerned," it said.

Over the past two years, H5N1 has been joined by newly detected H5N2, H5N3, H5N6 and H5N8 strains, all of which are currently circulating in different parts of the world.