If you'd rather not use vodka, don't worry - you can just sub it for water. The vodka is not there to provide alcohol content - it's for flavour, so it won't actually affect how the dish turns out other than a slight alteration to the taste. People use vodka in pasta sauce much in the same way that people use wine in pasta sauce. As it cooks off, all the alcohol disappears and most of the water evaporates, just leaving the flavour and sweetness behind.