Mediates the viral entry into the host cell together with fusion/F protein. Attaches the virus to sialic acid-containing cell receptors and thereby initiates infection. Binding of HN protein to the receptor induces a conformational change that allows the F protein to trigger virion/cell membranes fusion. Neuraminidase activity ensures the efficient spread of the virus by dissociating the mature virions from the neuraminic acid containing glycoproteins. Hydrolysis of alpha-(2->3)-, alpha-(2->6)-, alpha-(2->8)- glycosidic linkages of terminal sialic acid residues in oligosaccharides, glycoproteins, glycolipids, colominic acid and synthetic substrates. Homodimer (PubMed:12438628). Forms homotetramers (PubMed:15016893). Interacts with fusion/F protein (PubMed:14512552, PubMed:23740987). Interacts with host CG-1B; this interaction inhibits viral adsorption and replication rather than internalization (PubMed:28978647). Belongs to the paramyxoviruses hemagglutinin-neuraminidase family.