There is no vaccine though anti-malaria drugs offer some protection of sorts. I would avoid Larium: a close friend suffered terribly whilst on it, but would generally consult a doctor, preferably one who has practiced in a malaria-ravaged region. I'd follow all the other recommended precautions and get familiar with the early symptoms of malaria, as delayed presentation to a practitioner is of particular significance here. You may find this site useful. http://www.medicalgeek.com/lecture-notes/18023-complications-malaria.html

Otherwise, happy volunteering and enjoy East Africa!