Influenza is a seasonal respiratory virus of significant public health importance. Each year an estimated 3 to 5 million cases of severe influenza illnesses occur globally, and between 250,000 and 500,000 people will die as a result of their infection. The young, the elderly, pregnant women and people with comorbidities are at particular risk of severe infection (termed complicated influenza) and there are limited treatment options for these patients.
Intravenous (IV) zanamivir, which provides an additional treatment option for critically ill influenza patients, was approved for use in Europe in 2019, and a study – which is not conducted in CPRD – is currently underway to ensure that IV zanamivir is safe and effective in the real world.
The COVID-19 pandemic has had a large impact on influenza circulation, however, with the extremely low levels observed in the last two years making it difficult to recruit patients into the study.
The proposed feasibility study will help us understand the levels of hospital admission for influenza before and during the pandemic, which in turn will inform how the ongoing study can be changed to ensure success. This in turn will improve patient care in England & Wales by informing on the most appropriate treatment options for complicated influenza patients.
This study essentially replicates Protocol # 18_280 “Risk of hospitalised Influenza, England, 2000-2017”. It seeks to generate counts of patients admitted to hospital with influenza in England between 2011/12 and 2020/21 influenza seasons, inclusive. Influenza seasons will be defined as:
a) 1 October – 31 May (for example: 1 October 2011 – 31 May 2012, 1 October 2012- 31 May 2013, etc.).
b) 1 October – 31 March in addition to the definition above, since the most recent available data in CPRD-Hosppital Episode Statistics (HES) ends on 31 March 2021.
The numerator will be patients hospitalized with influenza in HES data. The denominator will be patients registered in CPRD practices that are linked to HES. Risk of hospitalization will be calculated as number of hospitalizations per 100,000 people per influenza season.
Counts for the numerators and denominators will be reported in total and stratified by broad age groups (<18, 18-64 & 65+ years), the primary nature of the hospital admissions (specifically, influenza was recorded as the primary reason for hospital admission vs not), the incident nature of the hospital admissions (specifically, if a patients had previous admissions for influenza in the 90 days prior to each admission vs not).
Index date will be defined as patients’ hospital admission date and will be used to calculate their age at admission and to determine if the admission was incident or prevalent (evidence of a previous flu admission respectively in the 90 days before each admission).
No formal statistical testing will be undertaken.
Influenza hospital admission, as defined by a record of an ICD-10 admission code for influenza (J09*, J10*, J11*).
Dina Christensen - Chief Investigator - GSK
Dina Christensen - Corresponding Applicant - GSK
Iain Gillespie - Collaborator - GlaxoSmithKline Research & Development Limited (UK)
Shinyoung Ju - Collaborator - GSK
HES Admitted Patient Care