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Influenza Vaccine Effectiveness Against Symptomatic Influenza in Primary Care: A Test Negative Case Control Study
Louise Marron1,2, Adele McKenna1, Joan O'Donnell1
1Health Service Executive, Health Protection Surveillance Centre, Dublin 1, Ireland.
Insights
Seasonal influenza vaccination significantly reduces the risk of influenza in primary care patients, especially children. Public health efforts should prioritize promoting the influenza vaccine, particularly the live attenuated influenza vaccine (LAIV) for pediatric populations.
Area of Science:
- Epidemiology
- Vaccinology
- Public Health
Background:
- Live attenuated influenza vaccine (LAIV) is recommended for children aged 2-17 years in Ireland.
- Quadrivalent influenza vaccine (QIV) is recommended for individuals aged 18+ with underlying conditions and those 65+.
Purpose of the Study:
- To estimate influenza vaccine effectiveness (IVE) against acute respiratory infection (ARI) presentations due to influenza in Irish primary care.
- To inform vaccination recommendations and public health communication campaigns.
Main Methods:
- A test-negative case control study was conducted within the Irish sentinel general practice surveillance network.
- Influenza vaccination status was compared between influenza PCR-positive cases and PCR-negative controls presenting with ARI.
- Logistic regression was used to estimate IVE, adjusting for age, onset time, medical conditions, and sex.
Main Results:
- In 2022/2023, overall IVE was 42% (95% CI 9 to 64), and 50% (95% CI -30 to 83) in 2- to 17-year-olds.
- In 2023/2024, overall IVE was 35% (95% CI 15 to 51), and 68% (95% CI 30 to 87) in 2- to 17-year-olds.
- Influenza vaccination demonstrated a protective effect against influenza in primary care ARI patients.
Conclusions:
- Influenza vaccination is effective in reducing influenza risk among patients presenting to general practice.
- Promoting seasonal influenza vaccination for recommended groups remains a public health priority.
- Vaccination campaigns for children should highlight the effectiveness of LAIV.
Introduction:
Live attenuated influenza vaccine (LAIV) is recommended in Ireland for all children aged 2-17 years. Quadrivalent influenza vaccine (QIV) is recommended for all others eligible for vaccination, including those ≥ 18 years with underlying medical conditions and all aged ≥ 65 years. We aimed to estimate influenza vaccine effectiveness (IVE) against acute respiratory infection (ARI) presentations to primary care due to influenza over two influenza seasons in Ireland, to inform vaccination recommendations and communication campaigns.
Methods:
We undertook a test-negative case control study within the Irish sentinel general practice surveillance network as part of the Vaccine Effectiveness Burden and Impact Studies (VEBIS) network. We compared influenza vaccination status among influenza PCR positive cases with influenza PCR negative controls, both with ARI presentations, of all ages. We estimated IVE using logistic regression adjusting for age, onset time, medical conditions and sex.
Results:
In 2022/2023, there were 288 cases and 765 controls. In 2023/2024, there were 567 cases and 1832 controls. In 2022/2023, overall IVE was 42% (95% CI 9 to 64) and 50% (95% CI -30 to 83) in 2- to 17-year-olds. Overall IVE in 2023/2024 was 35% (95% CI 15 to 51) and 68% (95% CI 30 to 87) in 2- to 17-year-olds.
Conclusion:
Influenza vaccination reduced the risk of influenza among ARI patients presenting to general practice, demonstrating the benefits of vaccination, particularly among children. Promotion of the seasonal influenza vaccine to recommended groups, should remain a public health priority. Targeted vaccination campaigns for children promoting LAIV should emphasise the effectiveness of LAIV in children.
