the 1968 hong kong virus was found to possess a haemagglutinin antigen markedly different from previous a2 strains but its neuraminidase is indistinguishable from the enzyme antigens of 1967-68 a2 viruses , and protection of mice immunized with 1957 and 1967 a2 viruse and challenged with hong kong virus was entirely attributable to antineuraminidase antibody .
C0003320
antigen
C0003342
antigens