There is less robust evidence for effectiveness in the populations targeted for influenza vaccination, but good evidence of vaccine effectiveness in healthy individuals. In the United Kingdom the live attenuated influenza vaccine has recently been recommended for children. The trivalent influenza vaccination is recommended for all ≥ 65 year olds and in individuals under 65 who are at an increased risk of complications of influenza infection e.g. people with asthma.
To examine the vaccine effectiveness of live attenuated influenza vaccine and trivalent influenza vaccination.
Test negative and cohort study designs to estimate vaccine effectiveness. A self-case series study to ascertain adverse events associated with vaccination.
A national linkage of patient-level general practice data from 230 Scottish general practices to the Scottish Immunisation Recall Service, Health Protection Scotland virology database, admissions to Scottish hospitals and the Scottish death register.
1.25 million people.
Live attenuated influenza vaccine for 2-11 year olds and trivalent influenza vaccination amongst older people (≥65 year olds) and under 65 years of age with at-risk diseases from 2010/11 to 2015/16.
Main outcome measures
Vaccine effectiveness against laboratory confirmed influenza using reverse transcription polymerase chain reaction (RT-PCR), influenza-related morbidity and mortality, adverse events associated with vaccination.
Two-fifths of pre-school (40%) and three-fifths (60%) of primary school children registered in our practices were vaccinated. Uptake varied amongst groups (e.g. most affluent vs. most deprived in 2-4 years odds ratio (OR) 1.76; 95%CI 1.70-1.82). Live attenuated influenza vaccine adjusted vaccine effectiveness amongst children (2-11 years) for preventing RT-PCR laboratory-confirmed influenza was 21% (95% Confidence Interval [CI] -19% to 47%) in 2014/15 and 58% (95%CI 39% to 71%) in 2015/16. No significant adverse events were associated with live attenuated influenza vaccine. Amongst at-risk 18-64 year olds significant trivalent influenza vaccination VE was found for four of the six seasons with highest vaccine effectiveness in 2010/11 (53%, 95%CI 21% to 72%). The seasons with non-significant vaccine effectiveness had low circulating influenza virus (2011/12: 5%; 2013/14: 9%). Amongst ≥ 65 year olds, trivalent influenza vaccination vaccine effectiveness was positive in all six seasons, but in only one of the six seasons (2013/14) was significance achieved (57%, 95%CI 20% to 76%).
Due to the observational nature of this study which used routinely collected data, residual confounding may have been present or unaccounted for.
We found that live attenuated influenza vaccinewas safe and effective in decreasing RT-PCR confirmed influenza in children. trivalent influenza vaccination was safe and significantly effective in most seasons for 18-64 year olds with positive vaccine effectiveness in most seasons for ≥65 year olds, although this was only significant in one season.
The UK Joint Committee on Vaccination and Immunisation have recommended the use of adjuvanted injectable vaccine for ≥65 year olds from season 2018/19 onwards. A future study will be required to evaluate this vaccine.
This project was funded by the National Institute for Health Research (NIHR) Health Technology Assessment programme.