Ok. There is a number of things wring with your code. First and foremost, your inequality signs are in the wring direction. No date value can be smaller than 01jan2010 and larger than 31dec2015...
I have written this template from the sashelp.stocks data set. Should give you what you want.
data test;
set sashelp.stocks;
prevalence = (('01jan1998'd <= date <= '31dec2000'd) and (stock='IBM'));
run;
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