Effectiveness of the trivalent MF59 adjuvated influenza vaccine in preventing hospitalization due to influenza B and A(H1N1)pdm09 viruses in the elderly in Italy, 2017 – 2018 season

Abstract

Q4 � Background: Evidence on influenza vaccine effectiveness (VE) in preventing mortality and morbidity in the elderly is weak. Our aim was to measure the VE against severe outcomes in the elderly. Methods: We conducted a multicentre hospital-based test-negative design (TND) case-control study, during the 2017/18 season, in four Italian hospitals. The study population included individuals aged ≥65 years hospitalized with Severe Acute Respiratory Infections (SARI). Patients were classified as cases and controls based on the results of the PCR influenza testing. We estimated VE by virus subtypes and specific VE for the trivalent adjuvanted vaccine (TIVadj). Results: 502 patients with SARI were enrolled: 118 (23.5%) tested positive (cases) and 384 (76.5%) tested negative (controls) for influenza. The adjusted VE of 48.5% for all vaccines was comparable to the adjusted VE for the TIVadj vaccine (48.3%). Adjusted VE for the TIVadj vaccine was 67.5% for A(H1N1) pdm09 and 44.5% for B viruses. Conclusion: We show a moderate adjusted VE of the TIVadj against all viruses, a good adjusted VE against A(H1N1)pdm09 strains and a moderate adjusted VE against B strains, despite a mismatch between the B circulating lineage and the lineage included in the vaccine. This is likely due to the crossprotection among B strains induced by the TIVadj in elderly patients.

Moderate Vaccine Effectiveness against Severe Acute Respiratory Infection Caused by A(H1N1)pdm09 Influenza Virus and No Effectiveness against A(H3N2) Influenza Virus in the 2018/2019 Season in Italy

“…In the ≥65 age group, adjusted VE against A(H1N1)pdm09 was around 48%. This is comparable to previously reported estimates of VE against severe influenza requiring hospitalisation in this age group during the 2017/18 season (data on hospitalised patients are not yet available for the 2018/19 season) [8,9].…”

“…During the 2017/18 season, a study was conducted in Italy to estimate VE of seasonal influenza vaccination, focusing specifically on SARI caused by the influenza virus, but the analysis was limited to people ≥65 years receiving a trivalent vaccine [9].…”

Adherence to Vaccination Policy among Public Health Professionals: Results of a National Survey in Italy

“…Nevertheless, PHPs' reported vaccination coverage for seasonal influenza in 2018/2019 was lower than the target of 75% to be achieved by 2015 put forth by the EU Council recommendation of December 2009 [51]. According to other studies, possible reasons to decline influenza vaccination may be its ineffectiveness [52,53] and fear of side effects [44].…”

Determinants of vaccination uptake, and influenza vaccine effectiveness in preventing deaths and hospital admissions in the elderly population; Treviso, Italy, 2014/2015-2016/2017 seasons

“…19 However, another study conducted during 2014/15 season in the same Italian Region of the previous study showed that the overall risk of death was 18% lower among vaccinated compared to unvaccinated subjects (21% for pneumonia and influenza). 18 A recent published test negative case-control study conducted in Italy during the 2016/17 season, to estimate vaccine effectiveness in preventing severe influenza in hospitalized elderly, 53 showed a good adjusted IVE of the MF59adjuvated vaccine against A(H1N1)pdm09 strains and a moderate adjusted IVE against B strains.…”