Out of 45,000 people, only 86ish people got infected in the trial arm? Isn't that too few? Even for the control arm, that's still only 774 people infected.
Those are the numbers that matter, statistically. If the total number of people in the study were 2 thousand or 2 billion doesn't enter into the math.
It affects confidence, and potentially the result of the test entirely. I won't be more specific because stats was never a strong suit and my memory's hazy, but I remember enough to know it matters!
It does seem low for the US where you have 3% of the population had disease already in 2020. Perhaps more data came from Germany? Or it could be they measure not just PCR +ve results, but antibody levels and/or severe symptoms?