Abstract
Influenza A virus infections are a global health threat to humans and are endemic in pigs, contributing to decreased weight gain and suboptimal reproductive performance. Pigs are also a source of new viruses of mixed swine, avian, and human origin, potentially capable of initiating human pandemics. Current inactivated vaccines induce neutralising antibody against the immunising strain but rapid escape occurs through antigenic drift of the surface glycoproteins. However, it is known that prior infection provides a degree of cross-protective immunity mediated by cellular immune mechanisms directed at the more conserved internal viral proteins. Here we review new data that emphasises the importance of local immunity in cross-protection and the role of the recently defined tissue-resident memory T cells, as well as locally-produced, and sometimes cross-reactive, antibody. Optimal induction of local immunity may require aerosol delivery of live vaccines, but it remains unclear how long protective local immunity persists. Nevertheless, a universal vaccine might be extremely useful for disease prevention in the face of a pandemic. As a natural host for influenza A viruses, pigs are both a target for a universal vaccine and an excellent model for developing human influenza vaccines.
Highlights
Influenza A virus infection is a global health threat to livestock and humans, causing substantial mortality and morbidity
These results suggest that live attenuated influenza vaccine (LAIV) offer partial cross-protection it is less efficient than infection with a live virus
The global influenza community is in urgent need of a universal influenza vaccine capable of inducing durable cross-protection against a broad spectrum of influenza virus strains
Summary
Influenza A virus infection is a global health threat to livestock and humans, causing substantial mortality and morbidity. FLU 3 (IDT Biologika, Dessau-Rasslau, Germany) and Gripovac (Merial, Lyon, France) against H1N1, H1N2, and H3N2 circulating SI viruses are used in approximately 5–25% of the pig farms in Belgium, Denmark, France, Spain, Italy, Poland, and Germany These vaccines do not protect against new viral strains and show poor efficacy in the field because of the evolution of the virus [9]. In contrast a double vaccination with an inactivated H1N1 and H3N2 based vaccine did not confer significant cross-protection [25], highlighting the importance of active virus replication for the induction of heterosubtypic immunity in pigs, directed towards the conserved internal proteins [26] In line with these findings partial protection was observed in pigs with infection-induced immunity against avian-like H1N1 upon challenge with. In this review we shall discuss the importance of local lung immunity and the feasibility of making an effective SI universal vaccine
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