Once the world is largely vaccinated then strains etc hopefully will be less of a concern.
the entire world is vaccinated? Do you want to go off and google vaccination rates in Chad, or Eritrea, or El Salvador? Developing countries can't afford to vaccinate everyone, never have, never will. Polio, which doesn't require an annual vaccine, still causes regular outbreaks in Africa. 6000 kids died of measles in the DR of the Congo a year ago.
I thought is was interesting that Jason Leitch brought up yellow fever. Yes some countries where yellow fever is an issue restrict entry and exit. You need a vaccination certificate. Yellow Fever is fatal in between 15% and 50% of cases. Covid is about 1%, or less. But we can't do the vaccination certificate thing because.... because we don't want to. Stay in Scotland. Enjoy the drizzle and midgies.