というNBER論文が上がっている（ungated版へのリンクがある著者の一人のページ）原題は「The Puzzling Behavior of Spreads during Covid」で、著者はStelios S. Fourakis（ジョンズホプキンズ大）、Loukas Karabarbounis（ミネソタ大）。
以下はその要旨。
Advanced economies borrowed substantially during the Covid recession to fund their fiscal policy. The Covid recession differed from the Great Recession in that sovereign debt markets remained calm and spreads barely responded. We study the experience of Greece, the most extreme manifestation of the puzzling behavior of spreads during Covid. We develop a small open economy model with long-term debt and default, which we augment with official lenders, heterogeneous households and sectors, and Covid constraints on labor supply and consumption demand. The model is quantitatively consistent with the observed boom-bust cycle of Greece before Covid and salient observations on macro aggregates, government debt, and the sovereign spread during Covid. The spread is stable despite a rise in external borrowing during Covid, because lockdowns were perceived as transitory and the bailouts of the 2010s had tilted the composition of debt at the beginning of Covid away from defaultable private debt. The ECB's policy of purchasing debt in secondary markets during Covid did not stabilize spreads so much, but allowed the government to provide transfers that reduced inequality.
（拙訳）
コロナ禍の景気後退において先進国は、財政政策を賄うためにかなりの借り入れを行った。コロナ禍の景気後退は、政府債務の市場が平穏なままに留まり、スプレッドがほとんど反応しなかった点で大不況と異なっていた。我々は、コロナ禍におけるスプレッドの奇妙な振る舞いが最も極端な形で現れたギリシアの推移を調べた。我々は、長期債務と債務不履行を備えた小さな開放経済モデルを構築し、それを公的な貸し手、不均一な家計と部門、およびコロナ禍による労働供給と消費需要への制約で拡張した。モデルは、コロナ禍前に観測されたギリシャの好不況循環、ならびにコロナ禍におけるマクロ変数、政府債務、国債スプレッドの顕著な観測結果と定量的に整合的であった。コロナ禍において対外借り入れが増えたにもかかわらずスプレッドは安定していたが、これはロックダウンが一時的なものと受け止められたことと、2010年代の救済によってコロナ禍が始まった時の債務構成のうち債務不履行となり得る民間債務が少なくなっていたことによるものだった*1。コロナ禍の期間中に流通市場で債務を購入するというECBの政策はそれほどスプレッドを安定させなかったが、それによって政府は格差を縮小させる移転所得が供給できた。
*1:これについて本文では以下のように書いている：「The second most important factor in generating a low spread during Covid is the old bailouts that Greece received during the 2010s. By old bailouts, we mean the official loans provided to Greece under the economic assistance programs. Whereas in the 2000s, less than 20 percent of Greek government debt was from official lenders, that proportion rose to more than 60 percent by the end of 2019. In a counterfactual world in which these loans had not been extended in the 2010s, Greece would have entered Covid with a debt composition that was tilted toward defaultable private debt, and the spread would have increased more during Covid. Similarly, as part of the economic adjustment programs in the 2010s, Greece wrote down less than half of its private debt. If prevailing policies had extracted more debt relief from private investors, expectations for future haircuts in 2020 would have been higher, and the spread would have increased by significantly more during Covid.」
