Laboratory tests have confirmed that the H7N9 bird flu found in China is resistant to the only known cure, AFP reported.
Three out of 14 patients who were being monitored at a clinic in Shaghai were infected with a genetically-mutated version of the virus that was resistant to the antiviral drugs used to treat it, a team of researchers in China wrote in the journal The Lancet.
One of the three patients infected developed a resistance after being treated with oseltamivir (Tamiflu), a widely used antiviral drug.
All of the patients had been given antiviral treatment, either Tamiflu or peramivir, which caused the virus levels to decrease in 11 patients.
Three of the patients had unusually high virus levels and had to be placed on oxygenated life support machines. Two of the patients died.
"The apparent ease with which antiviral resistance emerges in A/H7N9 viruses is concerning," the authors of the study wrote.
These are the first clinically confirmed cases of Bird Flu so far. Since the outbreak began in February a total of 130 people have been infected with the virus, and 37 have died from it.
The virus was originally thought to be spread from birds to humans, but recent studies have shown that the flu can be transmitted from mammal to mammal, and may even be able to spread between humans.
The bird flu is deadlier than the common virus and is characterized by severe pneumonia, fever, coughing and shortness of breath.
The study noted that two of the patients who's virus showed resistance had been treated with corticosteroids, which are often used to treat the flu. Researchers are now investigating the link between corticosteroids and resistance to see if the drug contributes to the cause of the mutation.
The agency has begun working on a strain-specific vaccine, but acknowledge that in the case of an epidemic the vaccine would be too late.
