No inoculations are mandatory for travel to Norway. A reciprocal agreement with the UK means hospital-in-patient treatment and ambulance travel is free.
Norway is one of the safest countries in Europe, however this shouldn't encourage complacency. Although only small, in comparison with most other capital cities, Oslo does have one big city problem, drugs. While governmental programs attempt to keep the problem off the streets there are some favoured city centre hang-outs for junkies. To this end the area west of Oslo S train station, towards Karl Johans gate(thoroughfare) is best avoided. Otherwise likelihood of encountering any crime is slim.