Setting Pendrive To Read Only Mode

Last week, my high school was infected with a virus. Every computer and pen drives were infected with it. At home, we don't have viruses problems often, because I'm cautious and my mom has a pen with a switch that enables and disables writing to her pendrive. Nowadays, it's rare to see such pens with such switches... So I wondered if there's anyway to, somehow, set my pen to 'read only' mode, so that when I plug it to public PCs, my pen doesn't get infected. And then, when I go home and connect the pen to my PC, have the capacity to write on it as usually.