highly significantp -values < 0.01
Comparison of the two groups before the first vaccination was given (time point 2) showed that significantly higher antibody levels were measured in the group with a preceding infection: These differences are highly significant for the full spike, S1, S2 and receptor-binding domains ( p -values < 0.01 in Wilcoxon rank-sum test; Figure 8 a and Figure S7 ).