Abstract
Every season, circulating influenza viruses change; therefore, vaccines must be reformulated each year. We aimed to estimate vaccine effectiveness (VE) against severe influenza infection for the 2018/19 season in Italy. We conducted a test-negative design case-control study at five Italian hospitals. We estimated influenza VE against severe acute respiratory infection (SARI) requiring hospitalisation overall, and by virus subtype, vaccine brand, and age. The 2018/19 season was characterised by A(H1N1)pmd09 and A(H3N2) influenza viruses. Vaccine coverage among <18 years recruited SARI cases was very low (3.2%). Seasonal vaccines were moderately effective against type A influenza overall (adjusted VE = 40.5%; 95% confidence interval (CI) = 18.7–56.4%) and subtype A(H1N1)pmd09 viruses (adjusted VE = 55%; 95% CI = 34.5–69.1%), but ineffective against subtype A(H3N2) viruses (adjusted VE = 2.5%; 95% CI = −50.0–36.7%). Both Fluad and Fluarix Tetra vaccines were effective against type A influenza overall and subtype A(H1N1)pdm09 viruses. VE appeared to be similar across age groups (0–64 years, ≥65 years). Seasonal influenza vaccines in the 2018/19 season were moderately effective in preventing SARI caused by A(H1N1)pdm09 influenza but ineffective against A(H3N2).
Highlights
Influenza is a major public health burden, accounting for up to 50 million disease episodes [1]and 72,000 deaths in Europe each year [2]
1693 patients with severe acute respiratory infection (SARI) were identified in the five participating centres
Seventeen patients were excluded because their vaccination status was unknown, six because their laboratory sample was taken >7 days after SARI onset, and one because they were vaccinated ≤14 days before presenting with SARI
Summary
Influenza is a major public health burden, accounting for up to 50 million disease episodes [1]and 72,000 deaths in Europe each year [2]. Influenza is a major public health burden, accounting for up to 50 million disease episodes [1]. The consequences of the influenza infection can be severe, both for the individual and for the health care system. The severity of the infection depends on the virus type/subtype, on host characteristics (e.g., age), and on other factors, such as access to care. Complications of influenza, such as pneumonia, are more common among specific risk groups, including elderly individuals, children under one year of age and people affected with immune deficiencies. Severe acute respiratory infection (SARI) caused by the influenza virus can result in hospitalisation [4]
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