Furthermore, the overall majority of H7 vaccines in the pipeline are focused on egg-based production which might be an inadequate platform in a pandemic setting due to limited manufacturing capacities and longer production times compared to cell-culture based systems. Based on predictions that consider the current maximum global capacity

for influenza virus vaccine Lumacaftor cell line manufacturing vaccine production will be too slow to adequately meet the needs for a vaccine in the event of a pandemic [36]. A major factor limiting the manufacturing capacity of a vaccine is the minimum immunogenic antigen dose that confers protection. It is highly desirable to obtain good efficacy already with low vaccine doses and the fewest possible injections to prevent shortages. Development of more efficient vaccines is a key objective defined by the Global Action Plan for Influenza vaccines by the WHO [37]. Here, we chose to evaluate a low-dose single-shot

VLP vaccine against the novel H7N9 virus. Single immunisation with as low as 0.03 μg SH1-VLP preparation (based on HA content) could confer full protection against a stringent homologous challenge (100 mLD50) in BALB/c mice (Fig. 1C). Mice that were vaccinated with a single vaccine dose of 3 μg SH1-VLP did not show any sign of disease. This is in contrast to an earlier study by Smith et al. who reported that mice vaccinated AZD5363 cell line with a two dose regimen with 0.7–2 μg lost 10–15% of their initial body weight after a 3.5 LD50 challenge [14]. Since the VLPs used in their study were highly purified we would speculate that active baculovirus contaminants

in our vaccine preparations (supplementary data) acted as an adjuvant and boosted the immune response – an effect that was reported before. It was shown that baculovirus can enhance immunogenicity of VLP vaccines through boosting the immune response by interferon-signalling Non-specific serine/threonine protein kinase and biasing IgG isotype distribution [16]. Vaccination with VLPs harbouring an HA from a closely related (but phylogenetically distinct) H7 strain, A/Anhui/1/13, also protected mice from PR8:SH1 challenge after only one immunisation. Generally, T-lymphocytes have long been appreciated as a critical contributor to protection and recovery from influenza infection [38]. Essentially, CD8+ T-cells play an important role in the clearance of virus infected cells and thereby limit viral replication, disease development and reduce mortality [26], [38] and [39]. We tended to address the importance of the cytotoxic immune response mediated by CD8+-cells in our challenge experiment. CD8+-depleted mice were fully protected in the challenge experiment and showed similar weight loss kinetics as observed for non-depleted mice (Fig. 1B and D), which is in agreement with previous findings [40]. However, in a recent work by Hemann et al.