[taipan100]

This is not really correct. CI means we are 95% sure that the true result falls somewhere within the range of -50 to 60. What this really means is that the study lacks statistical power to say anything interesting at all about vaccine effectiveness.

[willj]

Right. I phrased it a bit differently below. By “we can’t say” I meant that the study/researchers aren’t able to claim that the vaccine has non-zero effectiveness, i.e., they haven’t rejected the null.