Because the results of this trial is extremely convincing. The result of the Adecanumab trials was fairly unconvincing, and it was quite possible that the posit

Because the results of this trial is extremely convincing. The result of the Adecanumab trials was fairly unconvincing, and it was quite possible that the positive results were due to a fluke. The second reason is that Adecanumab did not (as far as I know) differ in approach to many other amyloid beta antibodies which have clearly failed to treat Alzheimer's in trials. Adecanumab binds to and clears amyloid beta tangles or plaques, but there is good evidence that the amyloid beta plaques are not really driving the disease. Lecanemab is different and specifically targets a form or conformation of amyloid beta. so called protofibrils, which are more much likely to be driving the disease process.