XK and infection: The moststriking effects were a 2000-fold enhanced infection inhibition anda ca. 100-fold enhanced lung retention of the divalent inhibitors.15 The results were confirmed in related studiesand even in animal studies,16−20 but interestingly, no multivalency effects were observed in theinhibition of the NA enzymatic activity by a monovalent MUNANA (4-methylumbelliferyl N-acetyl-α-d-neuraminic acid) probe.