Influenza virus poses a difficult challenge for protective immunity. This virus is adept at altering its
surface proteins, the
proteins that are the targets of
neutralizing antibody. Consequently, each year a new
vaccine must be developed to combat the current recirculating strains. A
universal influenza vaccine that primes specific memory cells that recognise conserved parts of the virus could prove to be effective against both annual
influenza variants and newly emergent potentially pandemic strains. Such a
vaccine will have to contain a safe and effective adjuvant that can be used in individuals of all ages. We examine protection from viral challenge in mice vaccinated with the
nucleoprotein from the PR8 strain of
influenza A, a
protein that is highly conserved across viral subtypes. Vaccination with
nucleoprotein delivered with a universally used and safe adjuvant, composed of insoluble
aluminium salts, provides protection against viruses that either express the same or an altered version of
nucleoprotein. This protection correlated with the presence of
nucleoprotein specific CD8 T cells in the lungs of infected animals at early time points after
infection. In contrast, immunization with NP delivered with
alum and the detoxified LPS adjuvant,
monophosphoryl lipid A, provided some protection to the homologous viral strain but no protection against
infection by
influenza expressing a variant
nucleoprotein. Together, these data point towards a
vaccine solution for all
influenza A subtypes.