Variable seasonal influenza vaccine effectiveness across geographical regions, age groups and levels of vaccine antigenic similarity with circulating virus strains: A systematic review and meta-analysis of the evidence from test-negative design studies after the 2009/10 influenza pandemic

• Published in: Vaccine 2021-02, Vol.39 (8), p.1225-1240
• Main Authors: Okoli, G.N., Racovitan, F., Abdulwahid, T., Righolt, C.H., Mahmud, S.M.
• Format: Article
• Language: English
• Subjects: Age; Antigens; Bias; Bibliographic data bases; Citations; Coronaviruses; COVID-19; Disease control; Disease prevention; Geographical distribution; Geographical locations; Health surveillance; Immunization; Influenza; Influenza A; Influenza B; Laboratories; Mathematical analysis; Meta-analysis; Northern Hemisphere; Pandemics; Public health; Seasonal influenza; Seasons; Similarity; Southern Hemisphere; Statistical analysis; Strains (organisms); Systematic review; Test-negative design; Vaccine effectiveness; Vaccine efficacy; Vaccines; Viruses
• ISSN: 0264-410X; 1873-2518
• DOI: 10.1016/j.vaccine.2021.01.032

•Vaccine performed best against A(H1N1)pdm09 & worst against A(H3N2) in all regions.•Overall, point pooled VE increased from Asia, to Europe, North America, & Oceania.•Overall, point pooled VE declined with age in the Northern hemisphere.•Considerably higher pooled VE with antigenically similar versus dissimilar vaccine.•Consistent patterns in VE across regions, age groups, vaccine antigenic similarity. We examined the influence of some factors on seasonal influenza vaccine effectiveness (VE) from test-negative design (TND) studies. We systematically searched for full-text publications of VE against laboratory-confirmed influenza from TND studies in outpatient settings after the 2009/10 influenza pandemic. Two reviewers independently selected and extracted data from the included studies. We calculated pooled adjusted VE across geographical regions, age groups and levels of vaccine antigenic similarity with circulating virus strains, using an inverse variance, random-effects model. We included 76 full-text articles from 11,931 citations. VE estimates against A(H1N1)pdm09, A(H3N2), influenza B, and all influenza were homogenous and point pooled VE higher in the Southern hemisphere compared with the Northern hemisphere. The difference in pooled VE between the Southern and Northern hemispheres was statistically significant for A(H3N2), influenza B, and all influenza. A consistent pattern was observed in pooled VE across both hemispheres and continents, with the highest point pooled VE being against A(H1N1)pdm09, followed by influenza B, and lowest against A(H3N2). A nearly consistent pattern was observed in pooled VE across age groups in the Northern hemisphere, with pooled VE mostly decreasing with age. Point pooled VE against A(H3N2), influenza B, and all influenza were statistically significantly higher when vaccine was antigenically similar to circulating virus strains compared with when antigenically dissimilar. Similar pattern was observed in the Northern hemisphere, but there was a lack of data from the Southern hemisphere. Consistent patterns appear to exist in seasonal influenza VE across regions, age groups, and levels of vaccine antigenic similarity with circulating virus strains, with best vaccine performance against A(H1N1)pdm09 and worst against A(H3N2). The evidence highlights the need to consider geographical location, age, and vaccine antigenic similarity with circulating virus strains when designing and evaluating influenza VE studies.