Vaccine effectiveness against influenza A(H3N2) and B among laboratory-confirmed, hospitalised older adults, Europe, 2017-18: A season of B lineage mismatched to the trivalent vaccine

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Influenza Other Respir Viruses. 2020 Feb 5. doi: 10.1111/irv.12714. [Epub ahead of print] Vaccine effectiveness against influenza A(H3N2) and B among laboratory-confirmed, hospitalised older adults, Europe, 2017-18: A season of B lineage mismatched to the trivalent vaccine.

Rose AMC¹, Kissling E¹, Gherasim A², Casado I³, Bella A⁴, Launay O^5,6, Lazăr M⁷, Marbus S⁸, Kuliese M⁹, Syrj?nen R¹⁰, Machado A¹¹, Kurečić Filipović S¹², Larrauri A², Castilla J³, Alfonsi V⁴, Galtier F^5,13, Ivanciuc A⁷, Meijer A⁸, Mickiene A⁹, Ikonen N¹⁴, G?mez V¹¹, Lovrić Makarić Z¹², Moren A¹, Valenciano M¹; I-MOVE Hospital study team.
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Abstract

BACKGROUND:

Influenza A(H3N2), A(H1N1)pdm09 and B viruses co-circulated in Europe in 2017-18, predominated by influenza B. WHO-recommended, trivalent vaccine components were lineage-mismatched for B. The I-MOVE hospital network measured 2017-18 seasonal influenza vaccine effectiveness (IVE) against influenza A(H3N2) and B among hospitalised patients (≥65 years) in Europe.
METHODS:

Following the same generic protocol for test-negative design, hospital teams in nine countries swabbed patients ≥65 years with recent onset (≤7 days) severe acute respiratory infection (SARI), collecting information on demographics, vaccination status and underlying conditions. Cases were RT-PCR positive for influenza A(H3N2) or B; controls: negative for any influenza. "Vaccinated" patients had SARI onset >14 days after vaccination. We measured pooled IVE against influenza, adjusted for study site, age, sex, onset date and chronic conditions.
RESULTS:

We included 3483 patients: 376 influenza A(H3N2) and 928 B cases, and 2028 controls. Most (>99%) vaccinated patients received the B lineage-mismatched trivalent vaccine. IVE against influenza A(H3N2) was 24% (95% CI: 2 to 40); 35% (95% CI: 6 to 55) in 65- to 79-year-olds and 14% (95% CI: -22 to 39) in ≥80-year-olds. Against influenza B, IVE was 30% (95% CI: 16 to 41); 37% (95% CI: 19 to 51) in 65- to 79-year-olds and 19% (95% CI: -7 to 38) in ≥80-year-olds.
CONCLUSIONS:

IVE against influenza B was similar to A(H3N2) in hospitalised older adults, despite trivalent vaccine and circulating B lineage mismatch, suggesting some cross-protection. IVE was lower in those ≥80 than 65-79 years. We reinforce the importance of influenza vaccination in older adults as, even with a poorly matched vaccine, it still protects one in three to four of this population from severe influenza.
? 2020 The Authors. Influenza and Other Respiratory Viruses Published by John Wiley & Sons Ltd.


KEYWORDS:

Europe; hospital; influenza; older adults; test-negative design; vaccine effectiveness

PMID: 32022450 DOI: 10.1111/irv.12714
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