Colorado's latest layer farm outbreak occurred not far from where culling workers were infected in a similar event.
Scientists said until the newer more closely matched vaccine is approved, earlier licensed vaccines might be a useful bridge, if needed.
Investigators are exploring if conditions in sweltering barns made PPE less effective and how the genotype infecting cows turned up on the poultry farm.
The avian flu in an elephant seal from Antarctica signals further expansion of the virus in the region's vulnerable wildlife.
In other developments, a challenge study in dairy cows finds that the virus can spread by both mammary and respiratory routes.
Colorado health officials are closely monitoring and testing workers, and the CDC has a field team on the ground to assist with the response.
Alongside more dairy herd confirmations, the USDA noted three more H5N1 outbreaks in poultry, all on Minnesota turkey farms.
The additional cat detections are from 2 states battling the virus in cows: Minnesota and Michigan.
The rise in invasive H influenzae disease came amid eased COVID measures, with babies and seniors the most affected groups.
The outbreak at the poultry farm, with more than 1.7 million birds, prompted an emergency declaration from Colorado's governor.
