Effectiveness of Trivalent Flu Vaccine in Healthy Young Children

Abstract

BACKGROUND: There are few studies evaluating the effectiveness of trivalent influenza vaccination (TIV) in young children, particularly in children <2 years. The Western Australian Influenza Vaccine Effectiveness Study commenced in 2008 to evaluate a program providing TIV to children aged 6 to 59 months. METHODS: An observational study enrolling children with influenza-like illness presenting to a tertiary pediatric hospital was conducted (2008–2012). Vaccination status was determined by parental questionnaire and confirmed via the national immunization register and/or vaccine providers. Respiratory virus polymerase chain reaction and culture were performed on nasopharyngeal samples. The test-negative design was used to estimate vaccine effectiveness (VE) by using 2 control groups: all influenza test-negative subjects and other-virus-detected (OVD) subjects. Adjusted odds ratios were estimated from models with season, month of disease onset, age, gender, indigenous status, prematurity, and comorbidities as covariates. Subjects enrolled in 2009 were excluded from VE calculations. RESULTS: Of 2001 children enrolled, influenza was identified in 389 (20.4%) children. Another respiratory virus was identified in 1134 (59.6%) children. Overall, 295 of 1903 (15.5%) children were fully vaccinated and 161 of 1903 (8.4%) children were partially vaccinated. Vaccine uptake was significantly lower in 2010–2012 after increased febrile adverse events observed in 2010. Using test-negative controls, VE was 64.7% (95% confidence interval [CI]: 33.7%–81.2%). No difference in VE was observed with OVD controls (65.8%; 95% CI: 32.1%–82.8%). The VE for children <2 years was 85.8% (95% CI: 37.9%–96.7%). CONCLUSIONS: This study reveals the effectiveness of TIV in young children over 4 seasons by using test-negative and OVD controls. TIV was effective in children aged <2 years. Despite demonstrated vaccine effectiveness, uptake of TIV remains suboptimal.

Viral Etiology and the Impact of Codetection in Young Children Presenting With Influenza-Like Illness

“…Influenza seasons each year were determined by influenza surveillance data in the state [13]. Children with a known immunodeficiency disorder, current or recent immunosuppressive treatment, or who received immunoglobulin in the previous three months were excluded from the study.…”

“…[13][14] and Discussion sections (p.14) concerning these results to clarify this point. Figures 2 and 3 also include 95% confidence intervals to minimise the risk of over-interpretation.…”

“…This study also enabled us to specifically examine the impact of viral-viral co-detection on clinical symptoms and outcomes. Further details on study design are described elsewhere [13].…”

Seasonal influenza vaccine effectiveness against medically attended influenza illness among children aged 6–59 months, October 2011–September 2012: A matched test-negative case–control study in Suzhou, China

“…The Guangzhou study also used database-verified vaccination history, but only included ILI cases, which might explain why their VE was slightly lower. Influenza vaccination is widely recognized as the most effective way to prevent influenza related diseases [21,22]. However, the effectiveness varies by year, depending upon the epidemic situation, and upon how well the circulating virus matches the vaccine virus types.…”

Observational studies and the difficult quest for causality: lessons from vaccine effectiveness and impact studies

“…• Measured and compared VE of pandemic and seasonal vaccines in various seasons documenting variation across seasons and sometimes across vaccines within a season in studies where classical controls were not employed (45,72,73) • In a few studies where different control groups were compared, VE estimates were sometimes similar for the test-negative design (74) and sometimes different (75); a comparison of perprotocol results from RCTs versus estimates from test-negative observational studies of an influenza vaccine and of an RSV monoclonal antibody showed close concordance (26) .…”