Influenza vaccine effectiveness in young children: Thailand Influenza Network for Evaluation (TINE) Open Access
Suntarattiwong, Piyarat (Fall 2018)
Abstract
The Thailand Influenza Network for Evaluation (TINE) was established to assess influenza vaccine effectiveness (VE) in the Thai population. During the 2017 Thailand influenza season (from June 1, 2017, through May 31, 2018), we applied a test-negative case-control design to evaluate the effectiveness of influenza vaccine against medically-attended, laboratory-confirmed influenza among children aged 6-36 months who presented at the seven participating hospitals in the TINE. To determine the evaluation period, all seven participating hospitals performed a rapid influenza test in children who presented with influenza-like-illness, at a rate of ten tests per week. The VE evaluation was conducted during periods when the proportion of positive rapid influenza tests from all hospitals combined was above 4%. For VE evaluation, we prospectively enrolled children 6-36 months seeking ambulatory care for acute respiratory illness (ARI) with onset ≤ 10 days. Consenting participants provided nasal and throat swabs for influenza real-time reverse transcription polymerase chain reaction (rRT-PCR) testing. Vaccination status was ascertained by vaccination booklets or hospital records. We applied a logistic regression model to determine the odds of PCR-confirmed influenza infection in vaccinated versus unvaccinated children. The VE was calculated as (1 – adjusted odds ratio) x 100.
We enrolled 2,823 children from July 23 through December 23, 2017, and 836 children from February 12 through April 12, 2018. Of 3,646 enrolled children with available influenza testing results for the VE analysis, 446 (12.2%) tested positive for influenza; of those, 310 (69.5%) were influenza A and 136 (30.5%) were influenza B. Influenza A(H3N2) and A(H1N1)pdm09 virus comprised 62.3% and 37.7% of influenza A positive tests respectively while influenza B-Yamagata lineage comprised 92.6% of influenza B positive tests. Influenza vaccination coverage was 6.8% and 4.7% for full vaccination and partial vaccination respectively. The VE against PCR-confirmed medically-attended influenza illness was 54.6% (95% confidence interval (CI): 23.0, 73.2) for full vaccination. The VE for influenza A(H1N1)pdm09, A(H3N2), and influenza B were 84.1% (95% CI: 34.6, 96.1), 50.4 (95% CI: -8.4, 77.4), and 15.4 (95% CI: -87.1, 61.8) respectively. According to the Thai National Influenza Center surveillance data, the reduced VE against influenza A(H3N2) is due to the antigenic drift of circulating influenza A(H3N2) virus to subclade 3C.2a1. And the VE against influenza B is likely to be impacted due to the fact that the predominant circulating influenza B was a Yamagata lineage virus while the influenza B composition of the trivalent influenza vaccine 2017 used in Thailand is a strain of influenza B-Victoria lineage virus. Overall, influenza vaccine provided moderate protection for Thai children during 2017 season. Additional efforts to increase vaccination coverage and continue effectiveness monitoring are warranted.
Table of Contents
Distribution Agreement……………………………………………………………………...…… i
Approval Sheet……………………………………………………………………………..……. ii
Abstract Cover Page…………………………………………………………….………………. iii
Abstract…………………………………………………………………………………………. iv
Acknowledgement……………………………………………………………………………… vii
List of Figures……………………………………………………………...……………………...x
List of Tables……………………………………………………………………….....………… xi
Chapter One: Introduction
Background and importance………………………………………………………………1
Chapter Two: Literature review
Influenza………………………………………………………………………………….7
The viruses………………………………………………………………………………...7
Clinical manifestations, diagnosis and treatment……………………………………….....8
Disease burden…………………………………………………………………………...10
Vaccination………………………………………………………………………………12
Assessing vaccine efficacy and effectiveness…………………………………………..16
Vaccine efficacy………………………………………………………………………….17
Vaccine effectiveness…………………………………………………………………….18
Influenza vaccine effectiveness (VE) studies in Southeast Asia…………………...…23
Chapter Three: Materials and methods
Population and sample…………………………………………………………………...31
Research design………………………………………………………………………….31
Study procedure………………………………………………………………………….34
Study instrument…………………………………………………………………………35
Sample size consideration and analysis plan…………………………………………….39
Ethical consideration……………………………………………………………………..40
Limitation and delimitation………………………………………………………………41
Chapter Four: Results
Enrollment………………………………………………………………………………..42
Influenza types, subtype, and lineage…………………………………………………....42
Vaccination status………………………………………………………………………..44
Characteristics of children……………………………………………………………….45
Characteristics of children by vaccination status………………………………………...46
Vaccine effectiveness (VE) estimates against laboratory-confirmed medically-attended influenza virus infection for full and partial vaccination………………………………...48
VE estimates against influenza A viruses by subtype and influenza B viruses………….49
VE estimates during the first and second peaks of influenza activity…………………...50
Sensitivity analysis……………………………………………………………………….51
Chapter Five: Discussion and Conclusion
Discussion and conclusion……………………………………………………………….53
References………………………………………………………………………………………..59
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