I’m pretty sure he said “sadly” because he’s acknowledging that...

I’m pretty sure he said “sadly” because he’s acknowledging that the vaccine has been a bit of a failure in that it took a long time to develop and distribute. And in that time, the virus mutated to a strain which did pretty much the same as the vaccine.

That’s my interpretation from the whole clip, not the just small part you quoted. Happy to be corrected.