Doctors have discovered antibodies to the mysterious 'bird flu' virus in the blood of nine Hong Kong people who never became seriously ill, health officials said Saturday.
Only one or two of the nine remember having had any flu symptoms, indicating that human resistance to the virus, which until recently only affected poultry, is not always as feeble as had been feared.
The presence of antibodies means a person has been exposed to the virus, and has developed resistance.
Among 11 people known to have developed full-blown flu from the virus, three have died. Eleven other people who have fallen sick are suspected of having the virus, and one of them has died.
Hong Kong health officials and doctors from the U.S. Centers for Disease Control and Prevention said that the blood tests did not answer the key question of how humans are contracting the virus.
Although mainland China says it has not found any trace of H5N1 infection in chickens on its farms, Hong Kong's top farm official, Lessie Wei, said he believes infected chickens found in local markets came from mainland China.