Pullet chicks were reared in isolation; all except a control group were variously vaccinated against infectious bronchitis. Individual haemagglutination inhibition (HI) antibody responses were measured from 1 day to 38 weeks old when all birds were challenged with virulent infectious bronchitis virus, and egg production recorded for a further 5 week period. In the controls HI titres remained low until challenge: this caused a loss of 15.1 eggs/hen. In birds injected with oil emulsion killed vaccine (OEV) at 3 and 16 weeks old, the serological response was uniformly high but on challenge the loss in egg production was 2.9 eggs/bird. Birds given H120 live vaccine at 3 weeks and H52 live vaccine at 15 weeks old had a low (23%) individual rate of serological response to the latter, and egg production after challenge was 3.63 eggs/hen less than before. In birds given H120 live vaccine at 3 weeks and emulsion killed vaccine at 16 weeks old, 100% serological response to the latter occurred and egg production was unaffected by challenge. A further group also received H120 and H52 live vaccines at 3 and 15 weeks old respectively: however, they were then subdivided into four groups and injected with emulsion vaccine at either 17, 19, 21 or 23 weeks old. Their response to H52 vaccine was variable. The proportion of birds in each sub-group responding serologically to subsequent vaccination with OEV was 45, 65, 73 and 92% respectively. After challenge egg production in these four sub-groups was reduced by 1.92, 1.15, 0.94 and 1.55 eggs/bird respectively. It is concluded that response to oil emulsion infectious bronchitis vaccine can be impaired if it is used within 8 weeks of H52 live vaccine. Best results are achieved where birds are given a primary dose of H120 live vaccine at 3 weeks old followed by emulsion vaccine 12-16 weeks later. Use of the less attenuated H52 strain of live vaccine before emulsion killed vaccine is contra-indicated.

Background A single intranasal (IN) dose of 108 TCID50 M2SR protected a responder subset of adults against infection and disease in a prior human influenza challenge study (EudraCT number: 2017-004971-30). Higher dose levels of M2SR were assessed in this phase 1b study to enhance immune responses and further increase protection levels in adults. Methods A double-blind, randomized, placebo-controlled dose escalation study (NCT03999554) was conducted at 4 US study sites with two different H3N2 M2SR vaccines that contained HA & NA from either A/Brisbane/10/2007 or A/Singapore/INFIMH-16–0019/2016. Serosusceptible 18–49 year old subjects (n = 206) received 2 IN doses of either saline or 1 of 3 different dose levels of vaccine (108 – 109 TCID50), administered 28 days apart. Results Study vaccination was well-tolerated at all dose levels. A single 109 dose of A/Singapore/2016 M2SR generated significantly increased serum HAI responses compared to the 108 dose of A/Brisbane/10/2007 M2SR that had provided protection against infection & illness in an earlier human influenza challenge study (Fig. 1). HAI titers ≥40 were achieved in 0%, 23% & 58% of subjects after the first dose of placebo, 108 or 109 M2SR, respectively (p< 0.003). Increases also were stimulated in serum microneutralization titers (MNT) to drifted strains of H3N2 (Fig 2) & in serum NAI (Fig 3) and mucosal sIgA (Fig 4) titers. Further increases in serum and mucosal immune response were noted after a 2nd IN vaccination. Proportion of subjects with seroprotective HAI titers after vaccination Proportion of subjects with increased microneutralization titers against drifted H3N2 viruses after vaccination Geometric mean fold rise in serum neuraminidase inhibition antibody titers after vaccination Conclusion An earlier clinical trial with a 108 dose of M2SR provided protection against infection and illness upon challenge with a highly drifted strain of H3N2. Protection correlated with vaccine induced serum MNT responses. In the current study, a single, 109 dose of M2SR significantly increased serum MNT, HAI & NAI titers as well as mucosal immune responses among greater proportions of study subjects. Since HAI, alone, is a well-accepted surrogate marker for vaccine protection against influenza, these broader enhancements indicate the potential for M2SR to protect against both matched and drifted strains of influenza in a high proportion of adults and strongly support clinical assessment in younger and older age groups as well as development of multivalent M2SR. Geometric mean fold rise in nasal mucosal secretory IgA antibody titers after vaccination Disclosures Joseph Eiden, MD, PhD, FluGen (Consultant) Ruth Ellis, MD, FluGen (Consultant) Roger Aitchison, ScM, FluGen (Consultant) Renee Herber, BS, FluGen (Employee) Pamuk Bilsel, PhD, FluGen (Employee)