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

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 cross-protection among B strains induced by the TIVadj in elderly patients.

KEYWORDS:

• Influenza vaccine effectiveness
• influenza trivalent vaccines
• TIVadj
• elderly
• hospitalized SARI cases

Article highlights

• Influenza adjusted vaccine effectiveness in elderly, community-dwelling patients hospitalised for Severe Acute Respiratory Infections was moderate for all vaccines (48.5%).

• As 94% of the vaccinated individuals included in our population had received the trivalent adjuvanted vaccine (TIVadj), we could calculate brand-specific figures.

• TIVadj showed a moderate adjusted VE against all viruses (48.3%); a good adjusted VE against A(H1N1)pdm09 strains (67.5%); a moderate adjusted VE against B viruses (44.5%)

• The moderate VE against B viruses, despite the lineage mismatch between the circulating strains and the strains included in the vaccine can be explain by the typical cross-lineage protection induced by the the TIVadj in elderly patients.

Acknowledgments

This project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement no. 634446. The study team is also very grateful to all patients, general practitioners, pediatricians, hospital teams, laboratory teams who have contributed to the study.

We thank Prof. Franco Laghi Pasini, Prof. Pierleopoldo Capecchi and Dr. Andrea Camarri (Scotte Hospital, Siena); Dr Iolanda Santino, Dr Filippo Di Ninno, Dr Andrea Petrucca, Dr Enrico Bertamino, Dr Alessandro Zerbetto (Department of Public Health and Infectious Diseases, University of Rome “Sapienza”, Italy); Simona Puzelli, Angela Di Martino, Marzia Facchini (Department of Infectious Diseases, National Institute of Health, Rome, Italy)

Author contributions

A Bella wrote the article and performed the statistical analysis, F Gesualdo wrote the article and contributed to the interpretation of results, A Orsi, C Arcuri, M Chironna, C Napoli, I Manini coordinated the study at the local level and revised the draft article, V Alfonsi and M R Castrucci supported the coordination of the study at the national level and revised the draft article, C Rizzo conceived the study, coordinated the study and wrote the article.

Declaration of interest

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

Reviewer disclosures

Peer reviewers on this manuscript have no relevant financial or other relationships to disclose

Additional information

Funding

This paper was funded by the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 634446.