COVID-19: Can a nurse legally refuse to work?

Nurses are presently working amid the COVID-19 pandemic. But can a nurse legally refuse to work? Most nurses are employed pursuant to a contract of employment. This is a legally binding arrangement between the employer and nurse. It sets out the terms (and there are implied terms also) concerning the legal obligations that both parties have towards each other. Of course, every contract cannot take into account every eventuality. Hence the terms of mutual obligation are drafted broadly and generically.