With no sample input, I will just guess and maybe it will help:
cat file
header for file
1111
header for file
1111
2222
header for file
3333
4444
5555
awk '/header/&&c++>0 {next} 1' file
header for file
1111
1111
2222
3333
4444
5555
Though I am not the greatest in sed
sed '1!{/^header/d;}' file
2
solved Bash: Remove all occurring pattern except 1