@article {Zhang2015,
	title = {Beta-interferon exposure and onset of secondary progressive multiple sclerosis},
	journal = {European Journal of Neurology},
	volume = {22},
	number = {6},
	year = {2015},
	pages = {990{\textendash}1000},
	publisher = {Wiley Online Library},
	doi = {10.1111/ene.12698},
	author = {Zhang, T and Shirani, A and Zhao, Y and Karim, ME and Gustafson, P and Petkau, J and Evans, C and Kingwell, E and Kop, M and Zhu, F and others}
}
