Officials don't know what caused gastrointestinal illness in 95 passengers and 9 crew on the Celebrity Eclipse in late December.
More than 50 counties in Arkansas have logged at least one case of whooping cough.
The patient has recovered after hospitalization, and no exposure to pigs or related illnesses have been found.
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.
