Safety and tolerability of cold-adapted influenza vaccine, trivalent, in infants younger than 6 months of age.

OBJECTIVE: Young children are at high risk for influenza-related complications. Vaccination of close household contacts is recommended to provide indirect protection to children <6 months of age. Studies have shown that live, cold-adapted influenza vaccine, trivalent, is efficacious in children. To assess the risks associated with inadvertent exposure of infants to vaccine viruses from vaccinated contacts, this study was designed to evaluate the safety and tolerability of cold-adapted influenza vaccine, trivalent, administered intranasally to healthy children 6 to <24 weeks of age. METHODS: Healthy infants aged 6 to <16 weeks and 16 to <24 weeks, respectively, were randomly assigned to receive 2 doses of influenza vaccine, or placebo intranasally 35 +/- 7 days apart. Reactogenicity events were monitored for 11 days after each dose. Other adverse events were monitored through 28 to 35 days after dose 2. RESULTS: Of the infants aged 6 to <16 weeks, 31 received influenza vaccine and 28 received placebo, and of those aged 16 to <24 weeks, 30 received influenza vaccine and 31 received placebo. In the 6- to <16-week cohort, more influenza vaccine, recipients experienced irritability (66.7% vs 35.7%) and runny nose or nasal congestion (63.3% vs 33.3%) after dose 1 but not dose 2. There were no significant increases in any other reactogenicity events or adverse events in the vaccine recipients compared with the placebo group. CONCLUSIONS: Although there was an increase in mild reactogenicity events in children 6 to <16 weeks of age, cold-adapted influenza vaccine, trivalent, was generally well tolerated in infants 6 to <24 weeks of age. These findings support further evaluation of cold-adapted influenza vaccine, trivalent, in infants <6 months of age.

Safety, efficacy, and effectiveness of cold-adapted influenza vaccine-trivalent against community-acquired, culture-confirmed influenza in young children attending day care.

OBJECTIVE: The goal was to evaluate the safety, tolerability, and efficacy of an investigational, refrigerator-stable formulation of live attenuated influenza vaccine (cold-adapted influenza vaccine-trivalent) against culture-confirmed influenza, acute otitis media, and effectiveness outcomes in young children in day care over 2 consecutive influenza seasons. METHODS: Children 6 to <36 months of age who were attending day care were assigned randomly in year 1 to receive 2 doses of vaccine or placebo intranasally, 35 +/- 7 days apart. In year 2, subjects received 1 dose of the same treatment as in year 1. RESULTS: A total of 1616 subjects (vaccine: 951 subjects; placebo: 665 subjects) in year 1 and 1090 subjects (vaccine: 640 subjects; placebo: 450 subjects) in year 2 were able to be evaluated for efficacy. The mean age at first vaccination was 23.4 +/- 7.9 months. In year 1, the overall efficacy of the vaccine against influenza subtypes similar to the vaccine was 85.4%; efficacy was 91.8% against A/H1N1 and 72.6% against B. In year 2, the overall efficacy was 88.7%; efficacy was 90.0% against H1N1, 90.3% against A/H3N2, and 81.7% against B. Efficacy against all episodes of acute otitis media associated with culture-confirmed influenza was 90.6% in year 1 and 97.0% in year 2. Runny nose or nasal discharge after dose 1 in year 1 was the only reactogenicity event that was significantly more frequent with cold-adapted influenza vaccine-trivalent (82.3%) than placebo (75.4%). CONCLUSIONS: Cold-adapted influenza vaccine-trivalent was well tolerated and effective in preventing culture-confirmed influenza illness in children as young as 6 months of age who attended day care.

A randomized, double-blind study of the safety, transmissibility and phenotypic and genotypic stability of cold-adapted influenza virus vaccine.

BACKGROUND: Live attenuated influenza vaccine (LAIV; FluMist) is a trivalent vaccine containing cold-adapted influenza vaccine viruses that infect and replicate in cells lining the nasopharynx to induce immunity. Recovery of viruses (shedding) is measured by culture of nasal specimens. Shedding of vaccine viruses is not equated with transmission because transmission requires more virus than is detected in many nasal swabs. Previous studies with LAIV did not detect transmission to close contacts. The primary objective of this study was to estimate the probability of transmission to placebo contacts in a day care setting. METHODS: One hundred ninety-seven healthy children aged 9 to 36 months attending day care were randomized to receive vaccine or placebo. Postvaccination viral shedding, safety, genotype and phenotype of shed viruses and probability of transmission were assessed. RESULTS: Eighty percent of 98 vaccine recipients shed at least one vaccine strain. No clinically significant differences in solicited adverse events attributable to vaccine occurred; safety profiles were similar in both groups. Vaccine virus isolates retained their phenotypic characteristics (cold adaptation and temperature sensitivity) and did not revert at nucleotides known to confer an attenuating phenotype. There was one confirmed transmission of a vaccine strain to a single placebo recipient. According to the Reed-Frost model, the calculated probability of transmission to a child after contact with a single vaccinated child was 0.58% (95% confidence interval, 0-1.7%). There was no increased reactogenicity or other safety concerns in the recipient child. CONCLUSIONS: Young children in a day care setting had a high rate of shedding and a low rate of transmission. No clinically significant illness occurred among children who received vaccine or placebo or in the child to whom the vaccine virus was transmitted.