Was thinking at weekend (it was the barbie that smelled of smoke) about the different strains of the virus and the longer term impact on immunity.
One reason for the common cold returning is that it doesn't make the patient ill enough to produce a strong immune response. Mutations are another but this could combine with the former.
Asia and western US have predominantly been infected with strain A that is less virulent or causes less extreme symptoms than strain C that has been the main form in Europe and eastern US. If a more extreme symptom can lead to a better immune response and the reverse is true -
- Is it possible that Europe/eastern US may develop a better immunity than Asia/western US?
- Is it possible that immunity to strain C (because of it's pathology) could lead to immunity to strain A while those countries hit with stain A and now at risk from strain C?
- Or maybe the reverse that as with smallpox/cowpox that using the weaker pathology agent can be used to vaccinate against the stronger?