The uncleaved viral hemagglutinin HA0 increases influenza A virus resistance to thermal pasteurization.

Two biological types of influenza virus are known and distinguished by the structure of the surface glycoprotein, hemagglutinin (HA). The noninfectious virions contain the uncleaved HA0 (80 kDa), whereas the infectious type have a cleaved form of two subunits, HA1 (55 kDa) and HA2 (25 kDa). The point cleavage of HA0→HA1+HA2 by host proteases regulates the virion integrity to maintain the functionality of the intravirion axis HA→M2→M1→RNP.