With @GrundSebastian and @COdendahl we have tried to build an instrument to share the fiscal costs of this crisis that is legally sound, economically sensible and institutionally feasible: The Pandemic Solidarity Instrument.

Tl;dr: https://voxeu.org/article/pandemic-solidarity-instrument-eu

Aim: make sure that all countries can do all the necessary fiscal spending to fight the economic fallout of the pandemic without getting overwhelmed by public debt.

Spending: The EU should give 440 bn in grants to member states for health costs; to subsidize short-time work schemes and unemployment benefits; to co-finance stimulus packages; and to prop up the EIB so that it can provide liquidity to companies everywhere in the EU.

Funding: The EU would issue bonds with long maturities in markets backed by member state guarantees. Bonds would either be refinanced perpetually or repaid later according to econ strength at time of repayment. Bonds would not add to debt of member states.

Legal base: Art. 122 TFEU. Legal act by the Council. Some national parliaments such as the Bundestag would need to ratify. No new institutions needed. EU already issues bonds. So can be up and running soon.