Clinical evaluation of neuraminidase monospecific (HEqN2) recombinant influenza vaccine in children.

Phased clinical trials were undertaken to evaluate the efficacy of neuraminidase specific recombinant (HEqN2) inactivated influenza vaccine in a population of school children. Groups of subjects were immunized under code, with influenza A2 Port Chalmer (H3N2), Port Chalmer neuraminidase recombinant (HEqN2), and placebo vaccines (vaccine diluent) before the onset of A2 strain influenza epidemic in this population. Preliminary results have provided the following information. Immunization with commercial Port Chalmer (H3N2) or neuraminidase recombinant influenza A2 (HEqN2) vaccines, in a childhood population was safe and without any major adverse effects. Vaccination with H3N2 vaccine regularly induced seronconversion for specific hemagglutination-inhibiting (HAI) antibodies in over 60% of vaccinated subjects. The mean titers of antineuraminidase antibody (ANAB) in H3N2 recipients who were seropositive prior to immunization increased five-fold while the ANAB titers of individuals who were seronegative prior to immunization did not rise significantly after immunization. On the other hand, immunization with HEqN2 vaccine resulted in little or no HAI response against H3, while specific ANAB response was observed in over 70% of such vaccines. The ANAB titers increased approximately 10 fold in the vaccines who were seropositive prior to immunization, and the titers in subjects seronegative prior to immunization were 5-6 fold higher than the post immunization titers observed in seronegative individuals in the H3N2 vaccinated group. Preliminary data on protection against natural reinfection suggested that, although the incidence of serological reinfection was similar in all vaccine groups, the expression of clinical disease was somewhat milder in HEqN2 vaccinees and in individuals with high levels of ANAB. These studies provide tentative support to the potential use of neuraminidase specific vaccine for mass immunoprophylaxis against influenza A2 virus.