Neuraminidase Antibody Response to Inactivated Influenza Virus Vaccine Following Intranasal and Intramuscular Vaccination

Background: The evaluation of influenza vaccine activity and potency are based on the immune response to hemagglutinin, and protection is indicated when the titer of hemagglutination inhibition serum antibody is ≥ 1:40. Neuraminidase, the second surface glyc c coprotein, may also have a role in protection, but little information is available on the immunologic response to this component. Objectives: To determine whether any response to neuraminic c dase is evoked by intranasal immunization with a novel, whole, inactivated anticinfluenza vaccine. Methods: This study was part of a more comprehensive study of mucosal and serum immune response to this vaccine. Fiftycfour young adults were immunized intranasally, 9 intramuscularly and 18 received a placebo. Twentycthree elderly people were immunized intramuscularly, and 21 elderly and 17 children were immunized intranasally. Serum and nasal antibodies to antigens N1 and N2 were determined by the lectin neuraminidase test. Results: Serum response following intranasal vaccination was lower than after intramuscular vaccination, and ranged from 21.4 to 35.3% and 33.3 to 64.7% following intranasal vaccination and from 52.2 to 77.8% and 47.8 to 88.9% after intramuscular vaccination, to N1 and N2 respectively. Nasal antibody response was low and was found only after intranasal vaccination, and response to N2 was better than to the N1 antigen. Conclusions: It may be beneficial if future vaccines would include competent hemagglutinin and neuraminidase, which would afford a higher level of protection.