I believe this is based on WHO data from laboratory-confirmed cases from the past 20 years or so. This is heavily biased toward more serious cases, as they would be the ones most likely to be noticed and tested. So the "real" mortality is likely a lot lower.
But "a lot lower" than 50% could still be pretty high.
I've seen a few sources say that H5N1 has something like a 50% mortality rate among humans - is that really true?
I believe this is based on WHO data from laboratory-confirmed cases from the past 20 years or so. This is heavily biased toward more serious cases, as they would be the ones most likely to be noticed and tested. So the "real" mortality is likely a lot lower.
But "a lot lower" than 50% could still be pretty high.