Blinded studies

Hi, I am learning statistics.
I have a question: how can one monitor safety data in an ongoing
double-blinded clinical trial? Suppose you have a series of subjects
from a trial (with an X total number of subjects) who present with
adverse events. All you have is the total number of subjects in the
trial (and the number of subjects for each treatment group; eg 1000
total subjects, 500 in each group and 35 present with an adverse event
E. I thought one way to monitor safety in a blinded way is to do a
comparison with previous similar trials (or background incidence rates
if available): like if a series of previous trials show that the
probability of having the event E was 0.02, then the probability of
the adverse event in the ongoing trial one is monitoring is
significantly greater than 0.02 (the background rate) and therefore
further steps could be taken.
Is this a sound approach or is it incorrect (or too simplistic)? What
better methods you suggested. All help is appreciated. Thanks.

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