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. 2015 Jul 22;10(7):e0132195.
doi: 10.1371/journal.pone.0132195. eCollection 2015.

Mid-Season Estimates of Influenza Vaccine Effectiveness against Influenza A(H3N2) Hospitalization in the Elderly in Quebec, Canada, January 2015

Rodica Gilca  1 , Danuta M Skowronski  2 , Monique Douville-Fradet  3 , Rachid Amini  3 , Nicole Boulianne  4 , Isabelle Rouleau  5 , Christine Martineau  6 , Hugues Charest  6 , Gaston De Serres  1
Affiliations

Mid-Season Estimates of Influenza Vaccine Effectiveness against Influenza A(H3N2) Hospitalization in the Elderly in Quebec, Canada, January 2015

Rodica Gilca et al. PLoS One. .

Abstract

Background: The 2014/15 influenza season in Canada was characterized by an early epidemic due to vaccine-mismatched influenza A(H3N2) viruses, disproportionately affecting elderly individuals ≥65-years-old. We assessed vaccine effectiveness (VE) against A(H3N2) hospitalization among elderly individuals during the peak weeks of the 2014/15 epidemic in Quebec, Canada.

Methods: Nasal specimens and clinical/epidemiological data were collected within 7 days of illness onset from elderly patients admitted with respiratory symptoms to one of four participating hospitals between November 30, 2014 and January 13, 2015. Cases tested RT-PCR positive for influenza A(H3N2) and controls tested negative for any influenza. VE was assessed by test-negative case-control design.

Results: There were 314 participants including 186 cases (62% vaccinated) and 128 controls (59% vaccinated) included in primary VE analysis. Median age was 81.5 years, two-thirds were admitted from the community and 91% had underlying comorbidity. Crude VE against A(H3N2) hospitalization was -17% (95%CI: -86% to 26%), decreasing to -23% (95%CI: -99 to 23%) with adjustment for age and comorbidity, and to -39% (95%CI: -142 to 20%) with additional adjustment for specimen collection interval, calendar time, type of residence and hospital. In sensitivity analyses, VE estimates were improved toward the null with restriction to participants admitted from the community (-2%; 95%CI: -105 to 49%) or with specimen collection ≤4 days since illness onset (- 8%; 95%CI: -104 to 43%) but further from the null with restriction to participants with comorbidity (-51%; 95%CI: -169 to 15%).

Conclusion: The 2014/15 mismatched influenza vaccine provided elderly patients with no cross-protection against hospitalization with the A(H3N2) epidemic strain, reinforcing the need for adjunct protective measures among high-risk individuals and improved vaccine options.

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Conflict of interest statement

Competing Interests: The authors have the following interests: RG has received research grants from Pfizer and from Sanofi for unrelated studies. GDS has received research grants from GlaxoSmithKline for unrelated studies and was reimbursed for travel expenses to attend an ad hoc GlaxoSmithKline advisory board meeting. There are no patents, products in development or marketed products to declare. This does not alter the authors' adherence to all the PLOS ONE policies on sharing data and materials.

Figures

Fig 1
Fig 1. Number of patients included in primary VE analysis by week of hospital admission date, and proportion of positive influenza tests in Quebec sentinel laboratory surveillance system, influenza season 2014/15.
Fig 2
Fig 2. Specimen inclusion/exclusion criteria for primary vaccine effectiveness analysis.
1Patients whom nurses were not able to approach because of early discharge or other operational considerations (i.e. workload demands during peak weeks of respiratory admissions); 2Symptoms onset >72h after hospital admission; 3Exclusions are not mutually exclusive; 415 respiratory syncytial viruses, 13 entero/rhinoviruses, 6 parainfluenza viruses, 2 coronaviruses, 1 human metapneumovirus
See this image and copyright information in PMC

References

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