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The Canadian Sentinel Practitioner Surveillance Network reports mid-season 2023/24 influenza vaccine effectiveness (VE) of 63% (95% CI: 51–72) against influenza A(H1N1)pdm09, lower for clade 5a.2a.1 (56%; 95% CI: 33–71) than clade 5a.2a (67%; 95% CI: 48–80), and lowest against influenza A(H3N2) (40%; 95% CI: 5–61). The Omicron XBB.1.5 vaccine protected comparably well, with VE of 47% (95% CI: 21–65) against medically attended COVID-19, higher among people reporting a prior confirmed SARS-CoV-2 infection at 67% (95% CI: 28–85).


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  1. Public Health Agency of Canada (PHAC). FluWatch report: January 7, 2023 to January 13, 2024 (week 2). Ottawa: PHAC; 2024. Available from: https://www.canada.ca/en/public-health/services/publications/diseases-conditions/fluwatch/2023-2024/week-2-january-7-january-13-2024.html
  2. Schmidt K, Ben Moussa M, Buckrell S, Rahal A, Chestley T, Bastien N, et al. National Influenza Annual Report, Canada, 2022-2023: Canada’s first fall epidemic since the 2019-2020 season. Can Commun Dis Rep. 2023;49(10):413-24.  https://doi.org/10.14745/ccdr.v49i10a02 
  3. De Serres G, Skowronski DM, Wu XW, Ambrose CS. The test-negative design: validity, accuracy and precision of vaccine efficacy estimates compared to the gold standard of randomised placebo-controlled clinical trials. Euro Surveill. 2013;18(37):20585.  https://doi.org/10.2807/1560-7917.ES2013.18.37.20585  PMID: 24079398 
  4. Government of Canada. COVID-19 vaccines: Canadian immunization guide. Ottawa: Government of Canada. [Accessed: 29 Jan 2024]. Available from: https://www.canada.ca/en/public-health/services/publications/healthy-living/canadian-immunization-guide-part-4-active-vaccines/page-26-covid-19-vaccine.html#t1
  5. World Health Organization (WHO). Recommended composition of influenza virus vaccines for use in the 2023-2024 northern hemisphere influenza season, Geneva: WHO; 2023. Available from: https://www.who.int/publications/m/item/recommended-composition-of-influenza-virus-vaccines-for-use-in-the-2023-2024-northern-hemisphere-influenza-season
  6. Canadian Sentinel Practitioner Surveillance Network (SPSN). Canadian Sentinel Practitioner Surveillance Network (SPSN) influenza vaccine effectiveness estimates % (95% CI), 2004-05 to 2022-23 seasons. Vancouver: SPSN; 2023. Available from: http://www.bccdc.ca/resource-gallery/Documents/Statistics%20and%20Research/Publications/Epid/Influenza%20and%20Respiratory/SPSN_VE_By_Year_Table.pdf
  7. Doll MK, Pettigrew SM, Ma J, Verma A. Effects of confounding bias in coronavirus disease 2019 (COVID-19) and influenza vaccine effectiveness test-negative designs due to correlated influenza and COVID-19 vaccination behaviors. Clin Infect Dis. 2022;75(1):e564-71.  https://doi.org/10.1093/cid/ciac234  PMID: 35325923 
  8. Firth D. Bias reduction of maximum likelihood estimates. Biometrika. 1993;80(1):27-38.  https://doi.org/10.1093/biomet/80.1.27 
  9. Heinze G, Schemper M. A solution to the problem of separation in logistic regression. Stat Med. 2002;21(16):2409-19.  https://doi.org/10.1002/sim.1047  PMID: 12210625 
  10. Devika S, Jeyaseelan L, Sebastian G. Analysis of sparse data in logistic regression in medical research: A newer approach. J Postgrad Med. 2016;62(1):26-31.  https://doi.org/10.4103/0022-3859.173193  PMID: 26732193 
  11. Zhou B, Donnelly ME, Scholes DT, St George K, Hatta M, Kawaoka Y, et al. Single-reaction genomic amplification accelerates sequencing and vaccine production for classical and Swine origin human influenza a viruses. J Virol. 2009;83(19):10309-13.  https://doi.org/10.1128/JVI.01109-09  PMID: 19605485 
  12. Aksamentov I, Roemer C, Hodcroft EB, Neher RA. Nextclade: clade assignment, mutation calling and quality control for viral genomes. J Open Source Softw. 2021;6(677):3773.  https://doi.org/10.21105/joss.03773 
  13. Rambaut A, Holmes EC, O’Toole Á, Hill V, McCrone JT, Ruis C, et al. A dynamic nomenclature proposal for SARS-CoV-2 lineages to assist genomic epidemiology. Nat Microbiol. 2020;5(11):1403-7.  https://doi.org/10.1038/s41564-020-0770-5  PMID: 32669681 
  14. Public Health Agency of Canada (PHAC). COVID-19 vaccination: Vaccination coverage. Ottawa: PHAC. [Accessed: 12 Feb 2024]. Available from: https://health-infobase.canada.ca/covid-19/vaccination-coverage/archive/2023-10-23/index.html
  15. Skowronski DM, Zou M, Sabaiduc S, Murti M, Olsha R, Dickinson JA, et al. Interim estimates of 2019/20 vaccine effectiveness during early-season co-circulation of influenza A and B viruses, Canada, February 2020. Euro Surveill. 2020;25(7):2000103.  https://doi.org/10.2807/1560-7917.ES.2020.25.7.2000103  PMID: 32098644 
  16. Tenforde MW, Kondor RJG, Chung JR, Zimmerman RK, Nowalk MP, Jackson ML, et al. Effect of Antigenic Drift on Influenza Vaccine Effectiveness in the United States-2019-2020. Clin Infect Dis. 2021;73(11):e4244-50.  https://doi.org/10.1093/cid/ciaa1884  PMID: 33367650 
  17. Rose A, Kissling E, Emborg HD, Larrauri A, McMenamin J, Pozo F, et al. , European IVE group. Interim 2019/20 influenza vaccine effectiveness: six European studies, September 2019 to January 2020. Euro Surveill. 2020;25(10):2000153.  https://doi.org/10.2807/1560-7917.ES.2020.25.10.2000153  PMID: 32183932 
  18. Smolarchuk C, Ickert C, Zelyas N, Kwong JC, Buchan SA. Early influenza vaccine effectiveness estimates using routinely collected data, Alberta, Canada, 2023/24 season. Euro Surveill. 2024;29(2):2300709.  https://doi.org/10.2807/1560-7917.ES.2024.29.2.2300709  PMID: 38214082 
  19. Altman MO, Angel M, Košík I, Trovão NS, Zost SJ, Gibbs JS, et al. Human influenza A virus hemagglutinin glycan evolution follows a temporal pattern to a glycan limit. MBio. 2019;10(2):e00204-19.  https://doi.org/10.1128/mBio.00204-19  PMID: 30940704 
  20. Skowronski DM, Chambers C, Sabaiduc S, De Serres G, Winter AL, Dickinson JA, et al. Beyond antigenic match: possible agent-host and immuno-epidemiological influences on influenza vaccine effectiveness during the 2015-16 season in Canada. J Infect Dis. 2017;216(12):1487-500.  https://doi.org/10.1093/infdis/jix526  PMID: 29029166 
  21. Raymond DD, Stewart SM, Lee J, Ferdman J, Bajic G, Do KT, et al. Influenza immunization elicits antibodies specific for an egg-adapted vaccine strain. Nat Med. 2016;22(12):1465-9.  https://doi.org/10.1038/nm.4223  PMID: 27820604 
  22. Liu F, Tzeng WP, Horner L, Kamal RP, Tatum HR, Blanchard EG, et al. Influence of immune priming and egg adaptation in the vaccine on antibody responses to circulating A(H1N1)pdm09 viruses after influenza vaccination in adults. J Infect Dis. 2018;218(10):1571-81.  https://doi.org/10.1093/infdis/jiy376  PMID: 29931203 
  23. Skowronski DM, Chuang ESY, Sabaiduc S, Kaweski SE, Kim S, Dickinson JA, et al. Vaccine effectiveness estimates from an early-season influenza A(H3N2) epidemic, including unique genetic diversity with reassortment, Canada, 2022/23. Euro Surveill. 2023;28(5):2300043.  https://doi.org/10.2807/1560-7917.ES.2023.28.5.2300043  PMID: 36729117 
  24. Skowronski DM, Kaweski SE, Irvine MA, Chuang ESY, Kim S, Sabaiduc S, et al. Risk of hospital admission and death from first-ever SARS-CoV-2 infection by age group during the Delta and Omicron periods in British Columbia, Canada. CMAJ. 2023;195(42):E1427-39.  https://doi.org/10.1503/cmaj.230721  PMID: 37903524 
  25. Bobrovitz N, Ware H, Ma X, Li Z, Hosseini R, Cao C, et al. Protective effectiveness of previous SARS-CoV-2 infection and hybrid immunity against the omicron variant and severe disease: a systematic review and meta-regression. Lancet Infect Dis. 2023;23(5):556-67.  https://doi.org/10.1016/S1473-3099(22)00801-5  PMID: 36681084 
  26. Tartof SY, Slezak JM, Frankland TB, Puzniak L, Hong V, Ackerson BK, et al. BNT162b2 XBB1.5-adapted vaccine and COVID-19 hospital admissions and ambulatory visits in US adults. medRxiv. 2023:2023.12.24.23300512. . https://doi.org/10.1101/2023.12.24.23300512 
  27. van Werkhoven CH, Valk A-W, Smagge B, de Melker HE, Knol MJ, Hahné SJ, et al. Early COVID-19 vaccine effectiveness of XBB.1.5 vaccine against hospitalisation and admission to intensive care, the Netherlands, 9 October to 5 December 2023. Euro Surveill. 2024;29(1):2300703.  https://doi.org/10.2807/1560-7917.ES.2024.29.1.2300703  PMID: 38179623 
  28. World Health Organization (WHO). Initial risk evaluation of JN.1, 19 December 2023. Geneva: WHO; 2023. Available from: https://www.who.int/docs/default-source/coronaviruse/18122023_jn.1_ire_clean.pdf?sfvrsn=6103754a_3
  29. Wang Q, Guo Y, Bowen A, Mellis IA, Valdez R, Gherasim C, et al. XBB.1.5 monovalent mRNA vaccine booster elicits robust neutralizing antibodies against emerging SARS-CoV-2 variants. bioRxiv. 2023:2023.11.26.568730. . https://doi.org/10.1101/2023.11.26.568730 
  30. Yang S, Yu Y, Xu Y, Jian F, Song W, Yisimayi A, et al. Fast evolution of SARS-CoV-2 BA.2.86 to JN.1 under heavy immune pressure. Lancet Infect Dis. 2024;24(2):e70-2.  https://doi.org/10.1016/S1473-3099(23)00744-2  PMID: 38109919 
  31. National Advisory Committee on Immunization. Statement on seasonal influenza vaccine for 2023-2024 Ottawa: Public Health Agency of Canada; 2023 [15 January 2024]. Available from: https://www.canada.ca/en/public-health/services/publications/vaccines-immunization/national-advisory-committee-immunization-statement-seasonal-influenza-vaccine-2023-2024.html#summary
  32. Waterhouse A, Bertoni M, Bienert S, Studer G, Tauriello G, Gumienny R, et al. SWISS-MODEL: homology modelling of protein structures and complexes. Nucleic Acids Res. 2018;46(W1):W296-303.  https://doi.org/10.1093/nar/gky427  PMID: 29788355 
  33. Schrödinger LLC. The PyMOL Molecular Graphics System. Version 2.5.2.

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