Unsurprising (to me). H5N1 causes variable disease severity, for a combination of reasons we don’t fully understand. Pathogenesis is never one size fits all.

If there are many human cases, some will be severe. Hence we need to stop human cases altogether.

https://www.cbc.ca/news/canada/british-columbia/first-presumptive-avian-flu-case-in-humans-1.7381342