...One of the challenges people foresaw with vaccines for a virus that mutates a lot like the flu is that the immunity against the spike protein might not work against mutant strains. But studies thus far have show that natural immunity is even more robust. A new preprint study from French researchers tested blood samples from health care workers who never had the virus but got both Pfizer shots against blood samples from those health care workers who had a previous mild infection and a third group of patients who had a serious case of COVID. They found, "No neutralisation...