Use awk command 'FNR==NR { array[$1,$2]=$8; next } ($1,$2) in array { print $0 ";" array[$1,$2] }' on compressed files "input1.vcf.gz" and "input2.vcf.gz"
gzip -dc input1.vcf.gz input2.vcf.gz | awk 'FNR==NR { array[$1,$2]=$8; next } ($1,$2) in array { print $0 ";" array[$1,$2] }'