The safety and efficacy of quadrivalent live attenuated influenza vaccine in Japanese children aged 2‐18 years: Results of two phase 3 studies

Background Quadrivalent live attenuated influenza vaccine (Q/LAIV) has not been assessed in Japanese children. Objectives Evaluate safety and efficacy of Q/LAIV in Japanese children. Patients/methods Two phase 3 studies were conducted in the 2014‐2015 influenza season. Study 1 was an open‐label, uncontrolled single arm, multicenter study of Q/LAIV safety in subjects aged 2‐6 years. Study 2 was a randomized, double‐blind, placebo‐controlled multicenter study of Q/LAIV safety and efficacy; subjects aged 7‐18 years were randomized 2:1 to receive Q/LAIV or placebo. Primary efficacy endpoint was laboratory‐confirmed symptomatic influenza infection caused by vaccine‐matched strains; secondary endpoint evaluated efficacy against all strains regardless of match. Both studies reported solicited symptoms, adverse events (AEs), and serious AEs. Results In Study 1, 100 subjects received Q/LAIV. In Study 2, 1301 subjects received Q/LAIV (n = 868) or placebo (n = 433). Treatment‐emergent AEs occurred in 42% of subjects in Study 1, and in 24.3% of subjects in the Q/LAIV arm and in 25.9% of subjects in the placebo arm in Study 2. In Study 2, a single infection by a vaccine‐matched strain was reported in the placebo arm, resulting in a vaccine efficacy estimate of 100% (95% CI: −1875.3, 100.0); efficacy for all strains regardless of match to the vaccine was 27.5% (95% CI: 7.4, 43.0). Conclusions Quadrivalent live attenuated influenza vaccine did not meet its primary efficacy endpoint as only a single infection by a vaccine‐matched strain was detected; however, efficacy for the secondary endpoint, all strains regardless of match, was achieved. Q/LAIV was generally well tolerated in the Japanese pediatric population.


| INTRODUC TI ON
Seasonal influenza affects an estimated 5%-10% of adults and 20%-30% of children worldwide. 1 In Japan alone, it is estimated that over 10 million people are infected with the influenza virus annually. 2 The global burden of influenza is substantial, and the World Health Organization estimates that influenza causes 3-5 million cases of severe illness and 300 000-500 000 deaths annually. 3 Children are at high risk of developing serious complications from influenza such as pneumonia and secondary bacterial infections, 4 and on a global level, influenza is associated with 10% of respiratory hospitalizations in children under 18 years old. 5 Influenza prevention is particularly important in those under 18 years of age, as children have the highest influenza attack rates 6 and are key transmitters of influenza in the community as they can shed a greater amount of virus for longer periods of time in comparison with adults. 7,8 In Japan, children have traditionally been vaccinated against influenza using trivalent inactivated influenza vaccines (TIVs) consisting of 3 influenza strains: two A strains and one B strain. However, 2 antigenically distinct lineages of influenza B (Victoria and Yamagata) commonly cocirculate in an influenza season. As Global Health Authorities have had limited success in selecting the B strain for trivalent vaccines that match the predominant circulating B strains, 9 it has been suggested that a switch from TIV to a quadrivalent vaccine could reduce the incidence of influenza infection. 10 The intranasally administered quadrivalent live attenuated influenza vaccine (Q/LAIV) contains 4 virus strains: two type A strains (A/H1N1 and A/H3N2), and two type B strains: one from each of the Victoria and Yamagata lineages. Q/LAIV is currently used in North America and several countries in Europe, including the United Kingdom, which has implemented a national pediatric vaccination program using Q/LAIV. 11 Although multiple studies have documented the safety and efficacy of Q/LAIV among children in countries outside Japan, [12][13][14] Q/LAIV has not previously been assessed in Japanese children.
Here, we report the results of two phase 3 clinical trials of Q/ LAIV in Japan: an open-label study of the safety and tolerability of Q/LAIV among Japanese children aged 2-6 years, and a randomized, double-blind, placebo-controlled study of the safety and efficacy of Q/LAIV among Japanese children aged 7-18 years.

| Study design
The first study (Study 1) was a phase 3 open-label, uncontrolled, multicenter study (ClinicalTrials.gov identifier: NCT02269488), which was conducted across 3 centers in Japan during the 2014-2015 influenza season to evaluate the safety and tolerability of Q/LAIV among Japanese children aged 2-6 years. The second study (Study 2) was a phase 3 randomized, double-blind, placebo-controlled multicenter study (ClinicalTrials.gov identifier: NCT02269475), which was conducted across 49 centers in Japan during the same influenza season to evaluate the safety and efficacy of Q/LAIV among Japanese children aged 7-18 years.
Both studies were performed in accordance with the principles of the Declaration of Helsinki, which are consistent with the International Conference on Harmonization (ICH)/Good Clinical Practice (GCP) and applicable regulatory requirements, and the AstraZeneca policy on Bioethics and Human Biological Samples.
Both protocols were approved by the Institutional Review Board (IRB) of each study center, and all participants and/or legal representatives provided written informed consent.

| Study 1
The study planned to enroll approximately 100 subjects aged 2-6 years to assess the safety and tolerability of Q/LAIV. All subjects received an initial intranasal administration of 0.2 mL (0.1 mL per nostril) of vaccine, while subjects not previously vaccinated against seasonal influenza received a second dose after an interval of at least 4 weeks. Healthy subjects and those with chronic underlying medical conditions including mild-to-moderate asthma were included, provided the subject had not been hospitalized in the previous year.
Subjects with asthma were included in this study and in Study 2 (below) based on the demonstrated safety and efficacy of LAIV in this population, 15 and as these subjects are included in the indicated populations who can receive Q/LAIV in Europe and Canada. 16,17

| Study 2
This double-blind study planned to enroll 1008 subjects aged 7-18 years to assess the safety and efficacy of Q/LAIV. Subjects were randomized (2:1) to receive Q/LAIV or placebo via intranasal administration. Subjects received an intranasal administration of 0.2 mL (0.1 mL per nostril). Subjects aged 7-8 years not previously vaccinated against seasonal influenza received a second dose after an interval of at least 4 weeks. Consistent with Study 1, healthy subjects and those with chronic underlying medical conditions were included, provided hospitalization was not required in the previous year.

| Determination of analysis set
In both Study 1 and Study 2, safety was assessed using the safety population, which included all subjects who received any amount of investigational product. For the safety population, subjects were analyzed per the treatment they received for the first dose. The perprotocol (PP) population was used for efficacy assessments in Study 2, and included all subjects who had no important protocol deviations, received the first and second dose of study vaccine or placebo per protocol, and were followed up for qualifying symptoms for influenza until the end of the influenza season.

| Safety and tolerability
In both Study 1 and Study 2, solicited symptoms were collected for 14 days post-vaccination and included the following: fever ≥100.4°F (38.0°C) by any route, runny/stuffy nose, sore throat, cough, headache, generalized muscle aches, decreased activity level or tiredness/ weakness, and decreased appetite. Adverse events (AEs), including treatment-emergent adverse events (TEAEs), were monitored for 28 days post-vaccination, and if patients received 2 doses of vaccine, they were monitored through the last dose. Serious adverse events (SAEs) were monitored from the time of informed consent through the last study contact with the subject.

| Efficacy
In Study 2, the primary efficacy endpoint was laboratory-confirmed symptomatic influenza infection (modified influenza-like illness per the Centers for Disease Control [mCDC-ILI]) caused by any community-acquired wild-type strains matched to the vaccine. The secondary efficacy endpoint was laboratory-confirmed symptomatic influenza infection (mCDC-ILI) caused by any communityacquired wild-type strains regardless of match to the vaccine.
Modified CDC-ILI was defined as increased temperature ≥100°F (37.8°C) (oral or equivalent) plus the presence of cough, sore throat, or runny nose/nasal congestion occurring on the same or consecutive days. Nasal swabs were evaluated for influenza using a polymerase chain reaction-based test, and genotyping, subtyping, and sequencing were performed. Isolates were categorized as vaccinelike (matched) or non-vaccine-like (mismatched) using genetic sequence alignment to reference strains for which a determination of match or mismatch was publicly available from the US CDC or other World Health Organization collaborating centers. For both efficacy endpoints, the influenza infection rate in Q/LAIV recipients was compared to that in placebo recipients during the influenza surveillance period and at least 14 days after the last administered vaccination.

| Statistical analyses
Categorical data were summarized by the number and percentage of subjects falling within each category, and continuous variables were summarized using descriptive statistics including mean, standard error or deviation, median, minimum, and maximum.
The primary and secondary efficacy endpoints evaluated vaccine efficacy, that is, the risk reduction of influenza infection in Q/LAIV recipients compared to placebo recipients calculated as one minus the ratio of the infection rates. Statistical comparison was made by constructing 2-sided 95% confidence intervals (CI) for the efficacy estimate, and the CI was estimated by an exact conditional method conditioning on the total number of cases, which followed a Poisson assumption. If the lower bound of the 95% CI of vaccine efficacy was >0%, then the efficacy of Q/LAIV was demonstrated.
In Study 1 and Study 2, all safety evaluations were descriptive in nature, and in Study 2, safety evaluations were provided by the dose number and by treatment group. AEs and TEAEs were summarized by system organ class (SOC) and preferred term (PT) using the Medical Dictionary for Regulatory Activities (MedDRA) version 17.1.
In both studies, statistical analysis was performed by Quintiles Transnational Japan K.K. in Japan. All analyses were conducted using Statistical Analysis System (SAS) version 9.2.

| Study subjects: Study 1
All 100 enrolled Japanese children aged 2-6 years completed the study and were included in the safety analysis. The mean (SD) age of subjects was 4.2 (±1.4) years and male subjects accounted for 45.0% (45/100 subjects) of the population (Table 1). Of the 100 subjects, 25.0% (25/100) had preexisting medical conditions; the most frequent conditions were asthma (14%), allergic rhinitis (5%), and dermatitis (5%). A majority of the 100 subjects enrolled had previously

| Study subjects: Study 2
A total of 1369 Japanese children aged 7-18 years were enrolled in Study 2. Of these, 1301 subjects were randomized to Q/LAIV (868) or placebo (433) with a 2:1 ratio at 49 study centers in Japan. Sixtyeight subjects were not randomized, primarily because randomization had closed after they were screened. All 1301 randomized subjects were included in the safety analysis.
The mean (SD) age of subjects was 11.0 (±3.0) years in the Q/ LAIV group and 10.8 (±2.8) years in the placebo group (

| Adverse events
In Study 1, during the 28 days after the first vaccination, TEAEs were noted in 42.0% (42/100) of subjects. Two of 6 subjects (33.3%) without previous influenza vaccination who received 2 doses of the vaccine experienced TEAEs during the 28 days after the second vaccination, and all TEAEs were mild in intensity (

| Efficacy
In Study 2, in the PP population, swab samples for genotyping, sub-

| D ISCUSS I ON
Children are at high risk of influenza infection compared with other age groups and play an important role in spreading influenza in the community. 8 The benefit of vaccinating children against influenza is twofold: a direct reduction of morbidity and mortality in the pediatric population, which can also extend to the community around them through reduced rates of secondary transmission. 18 In these first studies of the safety and efficacy of Q/LAIV in Japanese children, Q/LAIV was generally well tolerated, and the incidence of solicited symptoms and adverse events was similar to those observed in studies conducted outside of Japan. 19,20 The safety of

| CON CLUS IONS
The two phase 3 studies reported here provide the first assessment of the safety and efficacy of Q/LAIV in Japanese children. Q/LAIV was found to be generally well tolerated in the Japanese pediatric population 2 through 18 years of age, and the safety profile was comparable to that observed in studies conducted outside of Japan.
Observed efficacy was low, due to the predominance of circulating strains that were highly mismatched to the vaccine during the 2014-2015 season. Consequently, the study did not meet its primary efficacy endpoint, efficacy against matched strains, as only a single vaccine-matched strain was reported during the study. However, the secondary endpoint of efficacy against all strains regardless of match was met, and the results were consistent with LAIV efficacy observed in previous randomized trials in which significantly mismatched A/ H3N2 strains circulated.

ACK N OWLED G EM ENTS
The authors would like to thank the patients, their families, the investiga- Sponsor was involved in the study design, collection, analysis, and interpretation of data, as well as data checking of information provided in the manuscript. However, ultimate responsibility for opinions, conclusions, and data interpretation lies with the authors. Rito was an employee of AstraZeneca during this study.