Uptake of the Childhood Live Attenuated Influenza Vaccine (LAIV) and Influenza-related Healthcare Resource Use in England During the 2012 to 2022 Flu Seasons; a Retrospective, Observational Study in the CPRD and HES Databases
Condition: Influenza
MeSH terms: Influenza, Human
Study type: Observational

Summary: 
      In 2013, the NHS started a vaccination program in some regions of England to provide free flu
      vaccines to children aged 2 years or older, and younger than 16 years. The program has since
      been rolled out across England. Most children are given a vaccine that is sprayed into their
      nose. In clinical trials, this vaccine has been shown to protect children from experiencing
      severe flu symptoms. It is important to describe how it is used, and what happens to children
      who receive it in the wider community. This evidence will help the NHS to check that the
      vaccine roll out runs as planned and produces the intended benefits.

      This study aims to: (1) describe how many children each year receive flu vaccines, and
      describe the characteristics of children who are and aren't vaccinated for influenza; (2)
      test how often children receiving the vaccine see their GP or a hospital doctor for symptoms
      related to flu, compared to those who don't; and (3) to test what groups of children are more
      or less likely to receive a flu vaccine. To answer these objectives, the study will use the
      Clinical Practice Research Datalink, linked to Hospital Episode Statistics and the Office for
      National Statistics database.
    

Detailed description: 
      A Live Attenuated Influenza Vaccination (LAIV) has been offered to children through a rolling
      national program in England since 2013. Previous observational studies identified trends in
      LAIV uptake that varied with demographic and clinical profiles.

      The general aim of this study is to provide up-to-date epidemiological evidence on the uptake
      of the influenza vaccines, and influenza related HCRU outcomes in children in England. The
      specific study objectives are given below.

      Primary objective:

      1. To evaluate the uptake of influenza vaccines in children aged ≥2 and <18 years in England
      between 2012 and 2020 for LAIV, QIV, and influenza vaccinations where the product is not
      specified

      Secondary objectives:

      2.1 To describe usage patterns of LAIV in England between 2012 and 2020. 2.2 To describe HCRU
      associated with laboratory confirmed influenza and/or influenza-like-illness (ILI) in England
      between 2012 and 2020 and assess the relative impact of LAIV on HCRU use of LAIV vs no
      vaccination 2.3 To describe demographics and clinical characteristics of individuals
      vaccinated with LAIV or not vaccinated against flu by any vaccine in each flu season between
      2012 and 2020 2.4 To estimate a DAG aligned model for LAIV uptake in England based on
      demographic and clinical factors for each flu season and across multiple seasons between 2012
      and 2020

      The study will include all research eligible aged between ≥2 and <18 years in the study
      period, with 6 months of history in CPRD before their first influenza vaccination. It will
      use the Clinical Practice Research Datalink data (vaccinations, diagnoses, characteristics)
      linked to Hospital Episode Statistics (HCRU). Logistic regression analyses will be used to
      test for factors associated with vaccine uptake, and outcomes between vaccinated and
      unvaccinated children. The study will provide up-to-date epidemiological evidence on the
      uptake of LAIV and its impact on HCRU related to ILI in children in England. This may be used
      by the NHS for planning and evaluation of the childhood influenza vaccination program.
    

Observational model: Cohort
Time perspective: Retrospective
Sampling method: Non-Probability Sample
Study population: 
        The study will include all research eligible children born between the 1st January 1994 and
        31st August 2020 (latest date at which a child can be aged 2 years or above in the study
        period and have at least six months follow up in the most recent data), with 6 months of
        medical history available in CPRD before their the 1st September in the first year they are
        aged 2 years or above. The childhood influenza programme has been conducted on a rolling
        basis since 2013. Classification of each child as eligible for the vaccine will therefore
        vary year on year depending on their age, GP practice location and presence of high-risk
        conditions.