Here’s how the pandemic bonds worked.

The World Bank would sell $320 million of debt to investors. In the event of a pandemic, that debt would be written off and the principal would accrue to the bank to be distributed to needy countries. Premiums were juicy – the safest slice of the offering paid 6.9% over the Libor benchmark rate, similar to returns typically found on junk-rated corporate bonds and far greater than the 2.2% available on 10-year U.S. government debt at the time. For the second tranche, which had looser triggers for a writeoff, premiums were a whopping 11.5%.