The fact that previously infected people have higher titers to the vaccine implies nothing about the effectiveness of the vaccine -- it implies that the human i

The fact that previously infected people have higher titers to the vaccine implies nothing about the effectiveness of the vaccine -- it implies that the human immune system works, and recognizes the spike protein when it is re-introduced. Extrapolating from this to conclude that the protection is therefore better is an unsupported leap. The authors are trying to piggyback on previous work that claims that antibody levels correlate with immunity, but there's a huge difference between someone who has never had Covid, and someone who has. The abstract does say that vaccinated people have higher titers than naturally immune people, and this can be considered evidence: > mRNA vaccination induced much higher Ab levels especially against the RBD domain and significant cross-reactivity against SARS RBD and S1 was also observed.