They are people, and they can make mistakes or miss something, like everyone else.

A clear example is an Italian virologist that called the hypothesis of thrombosis in the alveoli that came out from autopsies and the suggestion of using heparin in treatment protocols "a colossal idiocy".

Then other data, including the recent Lancet paper and the Hamburg study came out.

The mere fact one is an expert does not make him or her always right. So weigh opinions more, but don't trust them blindly.