I do not think such a delay will happen as the financial costs are far too great to everyone:

A report published by the Economist Intelligence Unit last month projected that the bulk of the adult population of advanced economies would be vaccinated by the middle of next year. In contrast, this timeline extends to early 2023 for many middle-income countries and even as far out as 2024 for some low-income countries.

Source: Covid vaccine passports: Health experts are deeply concerned

BUT – it is a real possibility in a world where 15-days to flatten the curve has evolved to “until there are zero Covid cases worldwide”.

To put this risk in perspective, the year I had measles (and mumps at the same time), the case fatality rate for measles was 2.1%. Nothing was shut down. No one wore masks. People traveled freely.

By EdwardM