Abstract: A-influenza sub-unit vaccine is provided free from contaminants from A-influenza virus-containing allantoic fluid by a combination of selective membrane filtration and chemical splitting of the virus. The allantoic fluid first is freed of undesired particulate matter dimensioned smaller and larger than the virus and also of undesired dissolved matter. The virus then is chemically treated to split off the HA and NA units. Thereafter, the residual virus body, undesired particulates of same particle size as the virus, and a surfactant used in the chemical treatment are eliminated by selective membrane filtration. The procedure is much less costly and simpler to effect than prior art procedures.