The purpose of the present invention is to provide an antibody capable of inhibiting the infection of a cell with a norovirus. A nano antibody which contains a polypeptide as mentioned in (a), (b) or (c) and can inhibit the infection of an intestinal cell with HuNoV GII.3 and/or HuNoV GII.4: (a) a polypeptide comprising an amino acid sequence represented by SEQ ID NO: 1, SEQ ID NO: 5, SEQ ID NO: 9 or SEQ ID NO: 13； (b) a polypeptide comprising an amino acid sequence produced by substituting, deleting, inserting and/or adding one or several amino acid residues in an amino acid sequence represented by SEQ ID NO: 1, SEQ ID NO: 5, SEQ ID NO: 9 or SEQ ID NO: 13； and (c) a polypeptide comprising an amino acid sequence having a 80% or higher sequence identity to an amino acid sequence represented by SEQ ID NO: 1, SEQ ID NO: 5, SEQ ID NO: 9 or SEQ ID NO: 13.本發明之目的在於提供一種抑制諾羅病毒對細胞之感染之抗體，該抗體係一種奈米抗體，其係包含下述(a)、(b)或(c)中記載之多肽者，且抑制HuNoV GII.3及/或HuNoV GII.4對腸管細胞之感染。 (a)包含序列編號1、序列編號5、序列編號9或序列編號13所表示之胺基酸序列之多肽； (b)包含於序列編號1、序列編號5、序列編號9或序列編號13所表示之胺基酸序列中，置換、缺失、插入及/或附加1個或數個胺基酸而成之胺基酸序列之多肽；及 (c)包含與序列編號1、序列編號5、序列編號9或序列編號13所表示之胺基酸序列具有80%以上之序列同一性之胺基酸序列之多肽。
