How does introducing a vaccine late in the cycle of a seasonal illness make any sense anyway? If indeed covid 19 is like other flus and colds, by now most people either had it or shook it off. Remember that's a big if. However, if true, a reduction in cases will be attributed to the vaccine. What if the vaccine is totally worthless? Then new "breakthrough" cases will actually be new cases and there won't be many IF we are reaching herd immunity/end of infective spread cycle.