In a Vox column, Michal Kobielarz, Burak Uras and Sylvester Eijffinger argue that the  re-emergence of spreads between peripheral and core Eurozone countries at the beginning of the Greek crisis reflected contagion fears. They write:

… we explicitly model the endogenous bailout decision of the European Monetary Union. We assume that:

• A country that defaults on its sovereign debt can no longer remain in the EMU, unless it is bailed out;
• The union values each country’s membership and, therefore, suffers a loss if a country exits; and
• The marginal loss associated with allowing a country to leave the union is highest if that particular country is the first to leave (first-exit effect).

… once the first country is gone, letting a second country default and leave the union is not that costly anymore.