The effect of the current influenza vaccine, an inactivated virus vaccine administered by subcutaneous/intramuscular injection, is limited to reducing the morbidity and mortality associated with seasonal influenza outbreaks. Intranasal vaccination, by contrast, mimics natural infection and induces not only systemic IgG antibodies but also local secretory IgA (S-IgA) antibodies found on the surface of the mucosal epithelium in the upper respiratory tract. S-IgA antibodies are highly effective at preventing virus infection. Although the live attenuated influenza vaccine (LAIV) administered intranasally can induce local antibodies, this vaccine is restricted to healthy populations aged 2-49 years because of safety concerns associated with using live viruses in a vaccine. Instead of LAIV, an intranasal vaccine made with inactivated virus could be applied to high-risk populations, including infants and elderly adults. Normally, a mucosal adjuvant would be required to enhance the effect of intranasal vaccination with an inactivated influenza vaccine. However, we found that intranasal administration of a concentrated, whole inactivated influenza virus vaccine without any mucosal adjuvant was enough to induce local neutralizing S-IgA antibodies in the nasal epithelium of healthy individuals with some immunological memory for seasonal influenza viruses. This intranasal vaccine is a novel candidate that could improve on the current injectable vaccine or the LAIV for the prevention of seasonal influenza epidemics.
Keywords: intranasal administration; mucosal adjuvant; whole inactivated virus vaccine.