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smileylovesgaming The knowledge of this virus is still growing. There are some viruses that do need annual vaccinations, e.g. influenza, and covid may take on that model.
I totally disagree with your statement that it was inadequately tested, that is rubbish. As to why the virus persists, we have not had enough people vaccinated or having the natural disease to cause any sort of community immunity, and each infection and replication of the virus allows new mutants to appear, a mutation may develop a resistance to any antibody, either from a vaccine or the natural disease. It does appear that the current vaccines are more efficacious towards preventing serious disease, and that is important.
There is work on newer vaccines that may be more effective at preventing primary disease, they have been more difficult to develop. If you follow the average daily rates of infection and deaths, based on a sliding weekly average, the daily infections and deaths have been slowly creeping up again. We are at almost 500 daily US deaths! This is usually slow season for respiratory viral illnesses, I fear for what will happen in the fall.
We have limited ways to prevent the illness, vaccination, masking and social distancing is really all we have at this time.