The aim of this study is to determine responses of the immune system to the annual flu vaccination in people with COPD who experience frequent or infrequent exacerbations and healthy participants. We will collect blood and saliva immediately before and one month after flu vaccination at GP surgeries in the Autumn/Winter period. By measuring how quickly antibodies (that provide protection against infection) develop in the blood after vaccination we can provide important new information to help confirm whether those prone to COPD flare ups have weaker immune systems.

Inclusion Criteria:

Patients aged 65-85 years with a diagnosis of COPD (according to Global Initiative for Chronic Obstructive Lung Disease criteria: post bronchodilator FEV1/FVC ratio <0.70) and moderate to severe airflow limitation (FEV1 30-80% predicted) who opt to receive the annual influenza vaccine.

We will also include healthy participants aged 65-85 years without symptoms of lung disease who opt to receive the annual influenza vaccine.

Exclusion Criteria:

• Unable/unwilling to provide informed consent
• Any history of allergies, suspected hypersensitivity and/or contraindication to vaccines (e.g egg protein allergy)
• Participation in another clinical trial (use of investigational product or device)
• Not on optimal treatment (COPD patients only)
• Current smokers, exhaled CO >10 parts per million
• Clinical instability, defined as experiencing a COPD exacerbation less than 4 weeks prior to baseline visit, as indicated by treatment with systemic glucocorticosteroids and/or antibiotics and/or hospitalization (COPD only)
• An upper/lower respiratory tract infection e.g. common cold, sinus symptoms, pneumonia, which has not resolved four weeks prior to baseline visit
• Diagnosis of asthma and/or other relevant lung disease (e.g. history of primary or clinically significant bronchiectases, cystic fibrosis, bronchiolitis, lung resection, lung cancer, interstitial lung disease [e.g. fibrosis, silicosis, sarcoidosis], active tuberculosis)
• Known alpha-1-antitrypsin deficiency
• Immunological diseases or known infection with Human Immunodeficiency Virus (HIV)
• Any diagnosis of a malignant disease (other than basal or squamous cell carcinoma) in the last 5 years
• Currently taking immunosuppressive medications
• Diagnosis of diabetes mellitus
• Severe renal failure (calculated eGFR less than 60 ml/min)
• Liver impairment Child-Pugh B/C and/or active viral hepatitis
• Severe psychiatric or neurological disorders (Parkinson's disease or motor neurone disease)
• Planned donation of human tissue (blood, organs or bone marrow) during the course of the trial

Patients aged 65-85 years with a diagnosis of COPD (according to Global Initiative for Chronic Obstructive Lung Disease criteria: post bronchodilator FEV1/FVC ratio <0.70) and moderate to severe airflow limitation (FEV1 30-80% predicted) will be approached.

We will also include healthy participants as a control reference group who are aged 65-85 years without symptoms of lung disease and have normal spirometry.