highly significantP < 0·001
Whereas both blood group O and B patients possess circulating seric anti‐A, it appears and it is statistically highly significant ( P < 0·001) that O group patients are underrepresented (49·4 % vs. 57·6%), whereas B group patients are, on the contrary, overrepresented (50·6% vs. 42·4%), meaning that anti‐A from O is more protective than anti‐A from B.