> Outpatient treatment with metformin reduced long COVID incidence by about 41%, with an absolute reduction of 4.1%, compared with placebo.
The 4.1% is just decimal, using the middle-dot typographical version of decimal point.
Both figures are applicable and have different meanings. It's just a coincidence that they have the same digits this time.
Rough summary: The 41% is comparing the effect of metformin vs placebo metformin, both administered following protocols. It means nearly half of people (meeting the study criteria - age range, etc.) who would have got long Covid (as reported at 300 days) wouldn't get it if they took metformin following the protocol within 3 days of their positive Covid PCR test.
The 4.1% says how many fewer people got long Covid after getting Covid (and meeting the study criteria - age range, PCR test timing etc), that was attributable to having the real metformin. It doesn't tell you that it moved the needle from 10.4% of people (who had Covid etc) getting long Covid down to 6.3% (both as reported at 300 days). But it does tell you the difference between those figures, which is how many people's lives (4.1% of those people who had Covid etc) would likely be improved by taking it and following the protocol.
Is 4•1% some kind of notation?