By "expose somebody gradually to the virus" you're describing certain vaccine technologies.
Live viruses have a nasty habit of reproducing, spreading uncontrollably and killing a lot of people along the way. The people who survive do gain an immune response though.
Some virus technologies use "live-attenuated" vaccine, which are weakened (but living) versions of the virus which promote an immune response without causing illness.
Live viruses have a nasty habit of reproducing, spreading uncontrollably and killing a lot of people along the way. The people who survive do gain an immune response though.
Some virus technologies use "live-attenuated" vaccine, which are weakened (but living) versions of the virus which promote an immune response without causing illness.