Why? TLDR: Too small group and too few cases in groups (one each) to be statistical significant.
I said at the start not statistically significant. That is becuase they designed a shitty trial, if you are going to have an insignificant number of 65+'s in the trial, then dont make the target endpoint 'the number of cases' then when reporting a low efficacy are shocked when people took it on face value and ignored the p-value. If you want to test for side effects / will it kill people then make that the endpoint for that section of the trial.
That is horrifically bad science and communication. But if you publish a headline number of 70% efficacy in under 65's and 6.3% efficacy in over 65's what are you meant to think? That is might be quasi-ineffective in over 65s?