Multiple mutations have been found in the H5N1 bird flu virus that killed seven family members in Indonesia although scientists are unsure of their significance, a leading science journal said on Thursday.

“The functional significance of the mutations isn’t clear - most of them seem unimportant,” the journal Nature said in a report in the latest issue on Thursday.

An analysis of virus samples from six of the eight members of the family showed 32 mutations accumulated as it spread, according to the confidential research obtained by Nature. The analysis had been presented by virologist Malik Pereis of the University of Hong Kong at a closed meeting of animal and human health experts in Jakarta last month.

The first infected member of the family was a 37-year-old woman who probably caught the disease from poultry and then transmitted it to relatives before she died.

The World Health Organisation (WHO), which has admitted that the cluster of cases was probably caused by human-to-human transmission, had said in May that there had been no significant mutations in the strain found in the family.

Nature said although the WHO statement was not incorrect, more could have been said about the changes that were found.

“One of the mutations confers resistance to the antiviral drug amantadine, a fact not mentioned in the WHO statement,” the journal said.

The mutations found in the virus from the Indonesian cluster were not significant enough for the virus to spread beyond the family.

Virologists contacted by Nature said part of the reason the significance of the mutations is unclear is because withholding the information has hampered the study of the virus.

Scientists fear the H5N1 virus that has killed more than 100 people and millions of bird since 2003 as it spread from Asia to Europe and Africa could mutate into a strain that could spark a human pandemic.