Inactivated influenza vaccine for intranasal immunization

Influenza is a major winter contagious respiratory disease that takes a high toll on the population due to wide range morbidity, complications, hospitalization and mortality. At present, vaccination is the most effective means for controlling influenza infection. Licensed vaccines include several forms of inactivated vaccines (trivalent, quadrivalent, whole virus, split and subunit) delivered by injection with or without adjuvants, and live attenuated vaccines for intranasal administration (LAIV). Type of vaccine and mode of administration dictate the induced immune response and efficiency of vaccination. It has been suggested that intranasal administration induces better protection, as it neutralizes the virus at its entry site, eliciting production of secretory IgA (SIgA) antibodies and a serum barrier. In contrast, following injection, SIgA antibodies are produced only in negligible amounts. Another type of vaccine under clinical investigation is inactivated virus for intranasal application. This type of vaccine induces local (SIgA) and serum responses similar to the LAIV vaccines. Moreover, inactivated vaccines may be suitable for high-risk groups, which are constantly expanding, for whom live vaccines (approved only for healthy 2-49 years old) are inappropriate. The main obstacles toward successful vaccination are the annual changes in the virus (drift and occasional shift), appearance of new pandemic strains not included in the vaccine and transmission of pathogenic avian strains to humans. Efforts to develop a universal vaccine, which will protect against all A strains, might be a solution. Intranasal application of a universal vaccine to mice protected vaccinated animals from lethal infection by heterologous strains and furthermore reduced the transmission of virus from vaccinated to non-vaccinated mice. It may be concluded that intranasal inactivated virus formulas, either whole (without adjuvant), split (with adjuvant) or universal, may be the future vaccine for influenza.