Rose aphids (Macrosiphum rosae). The two backwards-facing tube are black, which confirms identification.
Not good for roses.
They carry viruses from plant to plant, and a large number on a rosebud will stop the flower forming.
What to do? search this forum for "rose aphids". If you have time you can rub them off with gloves into a bucket, natural predators can sometimes (only sometimes) keep the population low.
Not a health problem for humans - but the treatments can be.