Efficacy, immunogenicity, and safety of an oral influenza vaccine: a placebo-controlled and active-controlled phase 2 human challenge study.

BACKGROUND: Influenza is an important public health problem and existing vaccines are not completely protective. New vaccines that protect by alternative mechanisms are needed to improve efficacy of influenza vaccines. In 2015, we did a phase 1 trial of an oral influenza vaccine, VXA-A1.1. A favourable safety profile and robust immunogenicity results in that trial supported progression of the vaccine to the current phase 2 trial. The aim of this study was to evaluate efficacy of the vaccine in a human influenza challenge model. METHODS: We did a single-site, placebo-controlled and active-controlled, phase 2 study at WCCT Global, Costa Mesa, CA, USA. Eligible individuals had an initial A/California/H1N1 haemagglutination inhibition titre of less than 20 and were aged 18-49 years and in good health. Individuals were randomly assigned (2:2:1) to receive a single immunisation of either 1011 infectious units of VXA-A1.1 (a monovalent tablet vaccine) orally, a full human dose of quadrivalent inactivated influenza vaccine (IIV) via intramuscular injection, or matched placebo. Randomisation was done by computer-generated assignments with block size of five. An unmasked pharmacist provided the appropriate vaccines and placebos to the administrating nurse. Individuals receiving the treatments, investigators, and staff were all masked to group assignments. 90 days after immunisation, individuals without clinically significant symptoms or signs of influenza, an oral temperature of higher than 37·9°C, a positive result for respiratory viral shedding on a Biofire test, and any investigator-assessed contraindications were challenged intranasally with 0·5 mL wild-type A/CA/like(H1N1)pdm09 influenza virus. The primary outcomes were safety, which was assessed in all immunised participants through 365 days, and influenza-positive illness after viral challenge, which was assessed in individuals that received the viral challenge and the required number of assessments post viral challenge. This trial is registered with ClinicalTrials.gov, number NCT02918006. RESULTS: Between Aug 31, 2016, and Jan 23, 2017, 374 individuals were assessed for eligibility, of whom 179 were randomly assigned to receive either VXA-A1.1 (n=71 [one individual did not provide a diary card, thus the solicited events were assessed in 70 individuals]), IIV (n=72), or placebo (n=36). Between Dec 2, 2016, and April 26, 2017, 143 eligible individuals (58 in the VXA-A1.1 group, 54 in the IIV group, and 31 in the placebo group) were challenged with influenza virus. VXA-A1.1 was well tolerated with no serious or medically significant adverse events. The most prevalent solicited adverse events for each of the treatment groups after immunisation were headache in the VXA-A1.1 (in five [7%] of 70 participants) and placebo (in seven [19%] of 36 participants) groups and tenderness at injection site in the IIV group (in 19 [26%] of 72 participants) Influenza-positive illness after challenge was detected in 17 (29%) of 58 individuals in the VXA-A1.1 group, 19 (35%) of 54 in the IIV group, and 15 (48%) of 31 in the placebo group. INTERPRETATION: Orally administered VXA-A1.1 was well tolerated and generated protective immunity against virus shedding, similar to a licensed intramuscular IIV. These results represent a major step forward in developing a safe and effective oral influenza vaccine. FUNDING: Department of Health and Human Services, Office of the Assistant Secretary for Preparedness and Response, and Biomedical Advanced Research and Development Authority.

Production and Clinical Evaluation of Norwalk GI.1 Virus Lot 001-09NV in Norovirus Vaccine Development.

BACKGROUND: Human noroviruses (HuNoV) are the leading cause of gastroenteritis. No vaccine is currently available to prevent norovirus illness or infection. Safe, infectious challenge strains are needed to assess vaccine efficacy in the controlled human infection model (CHIM). METHODS: A stock of HuNoV strain Norwalk virus ([NV] GI.1) was prepared. Healthy, genetically susceptible adults were inoculated with NV Lot 001-09NV and monitored for infection, gastroenteritis symptoms, and immune responses. RESULTS: Lot 001-09NV induced gastroenteritis in 9 (56%) and infection in 11 (69%) of 16 genetically susceptible subjects. All infected subjects developed strong immune responses to GI.1 with a 30-fold (geometric mean titer) increase in blocking titers (BT50) and a 161-fold increase in GI.1-specific immunoglobulin (Ig)G titers when compared with baseline. GI.1-specific cellular responses in peripheral blood were observed 9 days postchallenge with an average of 3253 IgA and 1227 IgG antibody-secreting cells per million peripheral blood mononuclear cells. CONCLUSIONS: GI.1 Lot 001-09NV appears to be similar in virulence to previous passages of NV strain 8fIIa. The safety profile, attack rate, and duration of illness make GI.1 Lot 001-09NV a useful challenge strain for future vaccine studies aimed at establishing immune correlates.

Safety and immunogenicity of an oral tablet norovirus vaccine, a phase I randomized, placebo-controlled trial.

BACKGROUND: Noroviruses are the leading cause of epidemic acute gastroenteritis and foodborne diarrheal disease in humans. However, there are no approved vaccines for noroviruses. Potential correlates of protection identified through human challenge studies include mucosal IgA, memory B cells, and serum-blocking antibody titers (BT50). METHODS: We conducted a single-site, randomized, double-blind, placebo-controlled clinical trial of an oral norovirus vaccine to determine safety and immunogenicity. This tablet vaccine is comprised of a nonreplicating adenovirus-based vector expressing the VP1 gene from the GI.1 norovirus strain and a double-stranded RNA adjuvant. Sixty-six adult subjects meeting inclusion/exclusion criteria were randomized 2:1 to receive a single vaccine dose or placebo, respectively. Immunogenicity was primarily assessed by serum BT50. Additional outcomes included serum ELISA titers, fecal and saliva antibody titers, memory and antibody-secreting cell (ASC) frequency, and B cell phenotyping. RESULTS: The vaccine was well-tolerated, with no dose-limiting toxicities. Adverse events were mild or moderate. The primary immunological endpoint (increase in BT50 titers) was met in the high-dose group (P = 0.0003), with 78% showing a ≥2-fold rise in titers after a single immunization. Vaccine recipients also developed mucosally primed VP1-specific circulating ASCs, IgA+ memory B cells expressing gut-homing receptor (α4ß7), and fecal IgA, indicating substantial and local responses potentially relevant to prevent norovirus infection. CONCLUSION: This oral norovirus vaccine was well-tolerated and generated substantial immune responses, including systemic and mucosal antibodies as well as memory IgA/IgG. These results are a major step forward for the development of a safe and immunogenic oral norovirus vaccine. TRIAL REGISTRATION: ClinicalTrials.gov NCT02868073. FUNDING: Vaxart.

Persistent Sin Nombre virus infection in the deer mouse (Peromyscus maniculatus) model: sites of replication and strand-specific expression.

To address Sin Nombre (SN) virus persistence in deer mice, we sacrificed experimentally infected deer mice at eight time points from day 21 to day 217 postinoculation (p.i.) and examined their tissues for viral nucleocapsid (N) antigen expression and both negative-strand (genomic) and positive-strand (replicative/mRNA) viral S segment RNA titers. All the animals that we inoculated developed persistent infections, and SN virus could be isolated from tissues throughout the course of infection. The transition from an acute to a persistent pattern of infection appeared to occur between days 60 and 90 p.i. Beginning on day 60 p.i., the heart, brown adipose tissue (BAT), and lung retained antigen expression and genomic viral RNA the most frequently. We found a statistically significant association among the presence of replicative RNA in the heart, lung, and BAT, widespread antigen expression (in > or =5 tissues), and RNA viremia. Of these three tissues, the heart retained negative-strand RNA and viral N antigen the most consistently (in 25 of 26 animals). During persistence, there were two distinct patterns of infection: restricted versus disseminated tissue involvement. Mice with the restricted pattern exhibited N antigen expression in < or =3 tissues, an absence of viral RNA in the blood, neutralizing antibody titers of < or =1:1,280 (P = 0.01), and no replicative RNA in the heart, lung, or BAT. Those with the "disseminated" pattern showed N antigen expression in > or =5 tissues, neutralizing antibody titers of 1:160 to 1:20,480, replicative RNA in the heart, lung, and BAT at a high frequency, and RNA viremia. Virus could be isolated consistently only from mice that demonstrated the disseminated pattern. The heart, lung, and BAT are important sites for the replication and maintenance of SN virus during persistent infection.

Shedding and intracage transmission of Sin Nombre hantavirus in the deer mouse (Peromyscus maniculatus) model.

The mechanism(s) by which Sin Nombre (SN) hantavirus is maintained in deer mouse populations is unclear. Field studies indicate that transmission occurs primarily if not exclusively via a horizontal mechanism. Using an experimental deer mouse infection model in an outdoor laboratory, we tested whether infected rodents shed SN virus in urine, feces, and saliva, whether infected mice transmit infection to naïve cage mates, and whether infected dams are able to vertically transmit virus or antibody to offspring. Using pooled samples of urine, feces, and saliva collected from mice infected 8 to 120 days postinoculation (p.i.), we found that a subset of saliva samples, collected between 15 and 90 days p.i., contained viral RNA. Parallel studies conducted on wild-caught, naturally infected deer mice showed a similar pattern of intermittent positivity, also only in saliva samples. Attempts to isolate virus through inoculation of cells or naïve deer mice with the secreta or excreta of infected mice were uniformly negative. Of 54 attempts to transmit infection by cohousing infected deer mice with seronegative cage mates, we observed only a single case of transmission, which occurred between 29 and 42 days p.i. Dams passively transferred antibodies to neonatal pups via milk, and those antibodies persisted for at least 2 months after weaning, but none transmitted infection to their pups. Compared to other hantavirus models, SN virus is shed less efficiently and transmits inefficiently among cage mates. Transmission of SN virus among reservoir rodents may require factors that are not required for other hantaviruses.