Prevention of otitis media in children with live attenuated influenza vaccine given intranasally

The large enveloped RNA viruses remain the most common causes of serious infections of childhood. Influenza A and B, parainfluenza viruses and respiratory syncytial virus are the most common causes for hospitalization of infants and young children. Significant secondary diseases including otitis media (OM) often accompany these common viral infections, and viruses may be isolated from middle ear fluid in some cases. 1–3 Despite the availability of inactivated influenza virus vaccine for children and the demonstrated efficacy of this vaccine to prevent OM, inactivated influenza vaccine is infrequently used in this age group. 4 The recent demonstration that live attenuated intranasally administered vaccine is safe and effective in children and adults represents a new opportunity to reduce the impact of influenza and to prevent its complications, including pneumonia and OM in children. 5–7 This article summarizes the recent experience in children, with special emphasis on the prevention of OM and understanding the mechanisms of action of the live attenuated vaccine. METHODS Vaccine and placebo Trivalent cold-adapted influenza vaccine was supplied by Aviron (Mountain View, CA), frozen in single-dose intranasal applicators described below. In Year 1 the vaccine contained 106.7 tissue culture-infective dose (TCID)50/dose, and in Year 2, 107.0 TCID50/dose of each of the three attenuated strains that matched the antigens as recommended for the trivalent inactivated influenza vaccine by the Food and Drug Administration for the 1996 to 1997 and 1997 to 1998 influenza seasons, respectively. The vaccine was stored frozen at −20°C; thawed vaccine could be stored for up to 8 h at refrigerator temperature (2–8°C) before use. The placebo consisted of egg allantoic fluid containing sucrose-phosphate-glutamate and was indistinguishable in appearance or smell from the vaccine. The spray applicator consisted of a syringe-like device that was calibrated and divided for delivery of two 0.25-ml aliquots (one per nostril) as a large particle aerosol for a total delivered volume of 0.5 ml of study vaccine or placebo. Subjects The study population comprised 1602 healthy children ages 15 to 71 months at the time of initial vaccination in Year 1. Revaccination was offered to all available subjects from September through November, 1997. Of the original study group of 1602 children, 1358 (85%) were revaccinated with a single dose of live attenuated influenza vaccine by nasal spray. There were no statistically significant differences between the age, sex, race, day-care enrollment or household compositions of vaccine and placebo groups in Year 1 or Year 2. Informed consent was obtained from a parent or guardian. Children excluded from participation included those with a history of clinically significant hypersensitivity to eggs or children with underlying chronic illnesses for whom the inactivated influenza vaccine would be recommended. Study design The study was prospective, randomized, double blind, placebo-controlled and multicenter in design. The primary efficacy endpoint of the revaccination study was the first episode of culture-confirmed influenza illness in each year. Analyses included evaluation of subtype-specific efficacy, and in this case, all first cases of influenza A or influenza B were counted toward the subtype-specific efficacy. Subjects were randomized in a 2:1 ratio to receive vaccine or placebo and followed through the subsequent 2 influenza seasons. Volunteers were offered revaccination in Year 2 and were not rerandomized; subjects and staff remained blinded throughout the study. In Year 1 subjects at 8 of the 10 centers primarily received 2 doses of vaccine or placebo and 1 dose at the other 2 centers. In Year 2 subjects received 1 dose of vaccine or placebo. Two hundred three subjects participated in an immunogenicity substudy in Year 1; 159 of these children returned in Year 2, permitting characterization of strain-specific antibody responses to the vaccine. This cohort consisted of approximately the first 21 children recruited at each site for the efficacy study, and those volunteers had blood drawn before and 4 weeks after revaccination in Year 2. Reactogenicity A parent or a guardian of each subject was given a digital thermometer and asked to record on a diary card daily for 10 days the temperature of the subject and the occurrence of specific symptoms including decreased activity, irritability, runny nose, sore throat, cough, headache, muscle aches, chills or vomiting. Serious adverse events occurring at any time during the study were recorded by study personnel. Surveillance for influenza illness and case definitions Parents were contacted by telephone weekly during the influenza seasons (November through March) to remind them to notify study personnel if the subject developed symptoms suspected to be caused by influenza; these included fever, runny nose, nasal congestion, sore throat, cough, headache, muscle aches, chills, vomiting, suspected or diagnosed OM, decreased activity, irritability, wheezing, shortness of breath or pulmonary congestion. Report of any of these symptoms or signs resulted in a culture for viruses. Study sites attempted to collect viral culture specimens from symptomatic subjects within 4 days of onset of any illness. Rhesus monkey kidney tissue culture cells were inoculated with fresh respiratory secretions within 4 h of collection or as soon as possible thereafter to cultivate influenza viruses. The case definition of influenza was any illness detected by active surveillance (as described above) that was associated with a positive culture for wild-type influenza virus. Positive viral cultures obtained within 28 days of the annual revaccination were phenotyped to determine whether isolated viruses were wild-type influenza or were vaccine strain. Active surveillance for symptoms and signs of influenza captured a description of the illness including whether the child was seen by the primary care provider. The provider’s diagnosis and treatment were recorded. These diagnoses included lower respiratory disease and OM with or without concomitant fever and antibiotic treatment. The case definition of lower respiratory disease was any physician-diagnosed lower respiratory disease including croup, bronchitis, pneumonia or wheezing. The case definition of febrile OM was any health care provider diagnosis of OM associated with fever (either thermometer-documented or not). Serologic and secretory antibody studies Sera obtained from the immunogenicity cohort were stored at −20°C and assayed for the presence of hemagglutination inhibiting antibodies to the three viruses contained in the vaccine. 8 Additionally sera were assayed at Vanderbilt University for a range of hemagglutination inhibition antibodies to a panel of H3N2 viruses, including the inactivated vaccine strain A/Nanchang/933/95, the more recent isolate A/Sydney/5/97 and other divergent H3N2 viruses: A/Thessalonika/1/95, A/Russia/13919/95 and A/Johannesburg/33/94. 9 Antigens for this comparison were obtained from Dr. Roland Lewandowski (Food and Drug Administration, Bethesda, MD). Antibody titers of ≤1:4 were considered as representing seronegative children. Nasal washes were collected on the children participating in the immunogenicity substudy at Vanderbilt University and assayed for the presence of IgA, using a modified kinetic enzyme-linked immunosorbent assay as previously described. 10 In a parallel study conducted at Vanderbilt University, 31 seronegative children age 6 to 18 months were given the recommended 2 doses of inactivated trivalent influenza vaccine Fluzone (split); Connaught Laboratories, Swiftwater, PA. 9 Pre- and postvaccination sera from these children were used for the assessment of antibody responses to inactivated vaccine. For this comparison we tested sera from 25 children from the present study who were initially seronegative for H3N2 and compared antibody responses stimulated by 2 doses of live attenuated intranasal influenza vaccine to the antibody responses in the cohort of children described above who received 2 doses of trivalent inactivated vaccine. Data collection and statistical analyses Data were monitored on site and double data entered; adverse event diagnoses were COSTART (coding symbols for thesaurus of adverse reaction terms) coded 11 by Phoenix International Life Sciences (Irvine, CA). Statistical analyses used Statistical Analysis System (SAS) Version 6.12 and StatXact 2. 12, 13 Efficacy point estimates were computed as 100 · (1 − relative risk) = 100 · (1 −PV/PP);PV and PP = observed proportion of vaccine and placebo cases, respectively. Efficacy confidence intervals used Koopman’s method for the ratio of binomials. 13 The efficacy over both seasons was based on a child’s first case of influenza using a proportional hazards model and censoring children who dropped from the study between Year 1 and Year 2. The distribution of the number of illnesses per subject was compared with a Kruskal-Wallis test. Reactogenicity P values were adjusted separately for each vaccination and symptom by Bonferonni’s method. 13 Two sided P values are reported. RESULTS Safety No serious adverse events were associated with vaccination. Transient, minor symptoms of respiratory illness were present after Dose 1 of Year 1, when more vaccinated children, relative to placebo children, exhibited mild upper respiratory symptoms (rhinorrhea or nasal congestion (on Days 2, 3, 8 and 9 postvaccine), low grade fever (on Day 2 postvaccine) or decreased activity (on Day 2 postvaccine). 5 After revaccination no significant differences in rhinorrhea, fever or decreased activity were present. 6 Despite replication of vaccine virus in the upper airway, vaccination was not associated with OM (Table 1). When concomitant medications taken within 10 days of vaccine or placebo were compared for each dose in each year, only antipyretic use was significantly different (Year 1, Dose 1, 22% for vaccinees, 15% for placebo subjects, P 10 μm in diameter. Question: Upon administration do the vaccine particles go into the lower airway or do they stay in the nose? Dr. Belshe: In a study using radiolabeled albumin squirted through the intranasal device, all of the material was distributed in the upper airway of adults and volunteers. Question: Regarding attack rates in immunized children, are these truly infections in immunized children or were these vaccine failures who were infected? Dr. Belshe: Antibody studies were performed with a subset of children but we don’t really have the serum samples to examine all the vaccinated subjects. Breakthrough infections were significantly more mild in vaccinated children in terms of fever duration, 2 days in vaccinees vs. 5 days in placebo recipients. Question: How much of the vaccine impinges on the mucosa and how much is swallowed? Dr. Belshe: In a dose-ranging study subjects received either drops or spray. No significant difference was noted in vaccine responses in children. In adults the spray appeared to be a better immunogen than drops. It is likely that the spray is more widely distributed on the mucosal surfaces of the upper airways. Members of the Live Attenuated Influenza Vaccine Children’s Efficacy Trials Group include: Paul M. Mendelman, M.D., Iksung Cho, M.S., Keith Reisinger, M.D., John Treanor, M.D., Ken Zangwill, M.D., Frederick G. Hayden, M.D., David I. Bernstein, M.D., Karen Kotloff, M.D., James King, M.D., Pedro A. Piedra, M.D., Stan L. Block, M.D., Lihan Yan, MS, Janet Wittes, Ph.D., Gina Rabinovich, M.D., Mark Wolff, Ph.D. and Peter Wright, M.D.