There was a study in early/mid 2020 that tried to identify groups of mutations (what we now call "variants") and track their spread and severity over time. It f

There was a study in early/mid 2020 that tried to identify groups of mutations (what we now call "variants") and track their spread and severity over time. It found that most likely there was a mutation that started in or around Italy that increased the severity to the point excess death was easily detected, that then spread around the world. It was even noticeable in how it affected the US east and west coast differently, because the original out-of-Wuhan virus wasn't as severe. It was using identifiers like L, LL, and M; does this sound familiar to anyone? That early finding would completely explain the study you linked to.