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their efficacy against all symptomatic cases of the disease found in trials has been lower, ranging between 66% and 95%. Some of that range is down to intrinsic differences between the vaccines.
Source: The Economist
What does the bold text mean?
It clearly makes no sense if I understand "intrinsic differences between the vaccines" as the number of range.
"Down to" in this sentence is used to mean "a result of". See definition 12 of "down" here, where it's marked as chiefly British usage.
So the sentence means:
Some of the variance between 66% and 95% is caused by differences in the vaccines themselves.
