If you don't want to read the first line of the text file then use FIRSTOBS=2 option on the INFILE statement.
Also do NOT use formatted mode input for the first variable. Use LIST MODE like you did for the second variable. Add the : modifier in front of both informats.
data CoImpt.disabilities;
infile "/home/u63555769/Project/Data/1_Source/disabilities.txt" dlm='&' firstobs=2;
input tract_fips :$10. pctn_disability :$4.;
run;
Or remove the informats and DEFINE the variable before using them in the INPUT statement.
data CoImpt.disabilities;
infile "/home/u63555769/Project/Data/1_Source/disabilities.txt" dlm='&' firstobs=2;
length tract_fips $10 pctn_disability $4;
input tract_fips pctn_disability ;
run;