Ann: DSMB Recommends Continuation of Phase 3 COVID-19 Trial, page-239

Defining:
interim analysis = The analysis of data in a clinical trial comparing intervention groups at any time before the formal completion of the trial, typically before recruitment is
completed.
overwhelming efficacy =
Clinical study has shown that the predefined stopping boundary has been crossed and the candidates primary endpoint met.
I know the prelim data was shown to be very successful = 75% of patients off ventilation and discharged from hospital, but in reflection it seems the sample size is the real issue to extract a P value there needs to be a control group= is that which is blinded to treatment by placebo/candidate.
While the 1st prelim analysis is mostly for safety and efficacy - this was already a given due to product candidate being equal to Ryoncil [clinicals already proved safety]. The main decisions when first interim analysis from sample group is = Trial stop/continue for Safety then results from first analysis show no benefit = Trial stop/continue for Futility.
Given that the initial Mt Sinai hospital results would have been a defining "overwhelming efficacy" they must be discounted as no control group as compare to. I looked up a couple of P3 trials that were stopped early and looks like 2nd interim is the point where the patient sample size is enough to give a true picture of the P value analysis of treatment vs control group.
So it has been decided probably on the grounds that the group sample size @ 30% is too small to show the endpoints being met and we have a better chance that @ 45% or 135 patients the 2nd interim will provide the necessary key endpoint analysis. All in all it was a green light and a nice follow up to the announcement of Aust inclusion of patients to be treated with Remestemcel-L. 2 green lights in a week that shows the volatility in markets and the virus are not going away anytime soon.
Dips under 5 bucks well theres opportunity knocking but Nasdaq didn't boost MESO.
Ref
https://www.ahajournals.org/doi/pdf/10.1161/CIRCHEARTFAILURE.111.965707
https://www.ema.europa.eu/en/documents/presentation/presentation-sme-workshop-session-4-statistical-considerations-confirmatory-clinical-trials-ii_en.pdf