Experts say no bird flu vaccine is needed for humans yet, as mild cases among dairy workers don't warrant it. The current H5N1 strain shows low human transmission risk and responds well to antivirals.

"The Chinese poultry lineage may have experienced more vaccine-driven selection compared to other lineages," the researchers wrote.

H5N1 vaccines have been previously licensed, and millions are in the national stockpile. But even with the news of the country’s first human death due to bird flu, vaccination isn’t yet recommended.