Herd Immunity and Open Borders are Never Going to Happen, by David Evans.
Immunity to coronaviruses is too short-lived to get herd immunity:
Some cultures/counties around the world are not disciplined enough or wealthy enough to lockdown properly. Think particularly of large slums with closely packed people who have to work nearly everyday because they have no savings. And all the gradations, up to suburbs in wealthy countries that are spread out and can mostly go weeks or even months without work.
Those countries that do not lockdown enough will become reservoirs of the virus. Their people will only develop short term immunity to the virus, so they will catch it again every few years. So the virus will go on and on and on in those countries, culling the population continuously of those with underlying health conditions. Under Darwinian section, those countries will eventually become fitter.
Countries that do lockdown enough will almost eliminate the virus in their borders, keeping infections down to occasional flare-ups from outside. No culling of those populations.
Countries without the virus will not want any tourists or immigration from countries with the virus, without a two week quarantine. That might apply to all goods too. Borders will be strictly policed.
Along with the death of open borders, there will be a new potential for mischief. Countries or troublemakers with the virus might deliberately try to infect those without.
There is a real possibility of a fundamentally altered world, until there is a widely-applied biotech solution to COVID-19.