How many scientists have won the Nobel prize twice?

Four scientists have won a Nobel Prize twice. Those include:

Maria Sklodowska-Curie

1903 &1911, for discovery of radioactivity(Physics) and later for isolating pure radium (Chemistry).

John Bardeen

1958 & 1972, for invention of the transistor (Physics) and for coming up with the theory of superconductivity (Physics).

Linus Pauling

1954 & 1962 for research into the chemical bond in terms of complex substances (Chemistry) and for antinuclear activities (Peace).

Frederick Sanger

1958 & 1980 for the discovering the structure of insulin molecule (Chemistry) and inventing a method to determine base sequences in DNA (Chemistry).

Besides these:

The work of the International Committee of the Red Cross (ICRC) has been honoured by a Nobel Peace Prize three times.1917, 1944 and 1963.