But the researchers say other genetic mutations would likely be needed for the virus to prefer human cell receptors and enable efficient human transmission.
The source of the woman's infection isn't known.
So far 7 variant flu cases have been reported during the 2024-25 flu season in the US.
The state had reported an earlier similar case in March in a patient who had contact with pigs.
The results may guide choice of medications and aid surveillance efforts, the authors say.
Federal officials have been working with companies to find ways to boost the supply of the new vaccine for newborns.
Montana's H1N2v case was reported in a patient who had attended an agricultural fair.
For the first time, Argentina confirms H5 avian flu in mammals; also, Russia reports H5N1 at a large poultry farm.
The patient is a 42-year-old woman from Parana state who had underlying health conditions.
H9N2 avian flu has been confirmed in three children under 11, while H1N1v flu infected two preschool girls.
