Table 1.
Study characteristics of 83 articles that met eligibility criteria for assessment of current and previous season vaccine effectiveness
| Country | Design | Setting | Age range | Influenza virus type | Current season studied | Number of years previous vaccination | |
|---|---|---|---|---|---|---|---|
| Boddington et al (2019)42 | England | Test negative | Inpatient | 2–16 years | Any | 2015–16 | 1 |
| Buchan et al (2017)43 | Canada | Test negative | Inpatient | 6–59 months | A(H1N1)pdm09, A(H3N2), and B | 2010–11 to 2013–14 | 1 |
| Buchan et al (2018)44 | Canada | Test negative | Inpatient and outpatient | 2–17 years | A(H1N1)pdm09, A(H3N2), and B | 2012–13, 2013–14, 2014–15, and 2015–16 | 1 |
| Casado et al (2016)45 | Spain | Test negative | Inpatient | ≥65 years | Any | 2013–2014 | 1 |
| Casado et al (2018)46 | Spain | Case control | Inpatient | ≥65 years | Any | 2013–2014 and 2014–15 | 3 |
| Castilla et al (2011)47 | Spain | Nested case control | Inpatient and outpatient | All ages | Any | 2010–11 | 1 |
| Castilla et al (2016)48 | Spain | Test negative | Inpatient and outpatient | ≥6 months | A(H3N2) and B | 2014–15 | 2 |
| Castilla et al (2017)49 | Spain | Test negative | Inpatient and outpatient | ≥9 years | A(H3N2) | 2016–17 | 4 |
| Castilla et al (2018)50 | Spain | Test negative | Inpatient and outpatient | ≥9 years | A(H3N2) and B | 2017–18 | 5 |
| Castilla et al (2018)50 | Spain | Test negative | Inpatient and outpatient | ≥9 years | Any | 2017–18 | 5 |
| Castilla et al (2020)51 | Spain | Test negative | Inpatient and outpatient | ≥9 years | Any | 2018–19 | 3 |
| Cheng et al (2017)52 | Australia | Test negative | Inpatient | >9 years | A(H1N1)pdm09, A(H3N2), and B | 2011–15 | 1 |
| Dominguez et al (2017)53 | Spain | Case control | Inpatient | ≥65 years | Any | 2014–15 | 1 |
| El Omeiri et al* (2018)54 | Latin America | Test negative | Inpatient | ≥60 years | A(H1N1)pdm09 and any | 2013 | 1 |
| Ferdinands et al (2019)55 | USA | Test negative | Inpatient | ≥18 years | Any | 2015–16 | 1 |
| Flannery et al (2019)56 | USA | Test negative | Outpatient | ≥9 years | A(H3N2) and B | 2016–17 | 1 |
| Fu et al† (2015)57 | China | Case control | Outpatient | 3–6 years | A(H1N1)pdm09 | 2012–13 | 1 |
| Gaglani et al* (2016)58 | USA | Test negative | Outpatient | ≥50 years, 18–49 years, and 9–17 years | A(H1N1)pdm09 | 2013–14 | 1 |
| Gaglani et al* (2016)58 | USA | Test negative | Outpatient | ≥9 years | A(H1N1)pdm09 | 2013–14 | 1 and 4 |
| Gherasim et al† (2017)59 | Spain | Test negative | Outpatient | ≥9 years | A(H1N1)pdm09 | 2010–11, 2013–14, and 2015–16 | 1 |
| Gherasim et al† (2017)59 | Spain | Test negative | Outpatient | ≥9 years | A(H3N2) | 2011–12, 2013–14, and 2014–15 | 1 |
| Gherasim et al† (2017)59 | Spain | Test negative | Outpatient | ≥9 years | B | 2010–11, 2012–13, 2014–15, and 2015–16 | 1 |
| Grijalva et al (2021)60 | USA | Test negative | Inpatient | ≥18 years | Any | 2019–20 | 1 |
| Jackson et al* (2017)61 | USA | Test negative | Outpatient | ≥9 years | A(H1N1)pdm09, and B/Victoria, and B/Yamagata | 2015–16 | 1 |
| Jiménez-Jorge et al (2012)62 | Spain | Test negative | Outpatient | 0–95 years | A(H1N1)pdm09 | 2010–11 | 1 |
| Kim et al* (2021)38 | USA | Test negative | Outpatient | ≥9 years | A(H1N1)pdm09 | 2013–14 and 2015–16 | 1 |
| Kim et al* (2021)38 | USA | Test negative | Outpatient | ≥9 years | A(H3N2) | 2012–13, 2014–15, 2016–17, and 2017–18 | 1 |
| Kim et al* (2021)38 | USA | Test negative | Outpatient | ≥9 years | B | 2012–13, 2014–15, 2015–16, 2016–17, and 2017–18 | 1 |
| Kissling et al* (2018)63 | Europe | Test negative | Outpatient | ≥9 years | A(H1N1)pdm09 | 2015–16 | 1 |
| Kissling et al* (2018)63 | Europe | Test negative | Outpatient | 15–64 years | B | 2015–16 | 1 |
| Kissling et al* (2019)64 | Europe | Test negative | Outpatient | ≥9 years | A(H3N2) | 2018–19 | 1 |
| Kissling et al* (2019)65 | Europe | Test negative | Outpatient | ≥9 years | A(H1N1)pdm09 | 2017–18 | 1 |
| Kissling et al* (2019)65 | Europe | Test negative | Outpatient | ≥9 years | A(H3N2) | 2016–17 and 2017–18 | 1 |
| Kwong et al (2020)66 | Canada | Test negative | Inpatient and outpatient | >65 years | Any | 2010–11 to 2015–16 | 1 |
| Kwong et al (2020)66 | Canada | Test negative | Inpatient and outpatient | ≥70 years | Any | 2010–11 to 2015–16 | 5 |
| Kwong et al (2020)66 | Canada | Test negative | Inpatient and outpatient | ≥75 years | Any | 2010–11 to 2015–16 | 10 |
| Ma et al (2017)67 | China | Test negative | Outpatient | ≥6 months | Any | 2014–15 | 1 |
| Martinez-Baz et al (2013)68 | Spain | Test negative | Inpatient and outpatient | ≥6 months | A(H1N1)pdm09 | 2010–11 | 1 |
| Martinez-Baz et al (2017)69 | Spain | Test negative | Inpatient and outpatient | ≥6 months | A(H1N1)pdm09 | 2010–11, 2012–13, 2013–14, and 2015–16 | 1 |
| Martinez-Baz et al (2017)69 | Spain | Test negative | Inpatient and outpatient | ≥9 months | A(H1N1)pdm09 | 2010–11, 2012–13, 2013–14, and 2015–16 | 1–6 |
| Martinez-Baz et al (2021)70 | Spain | Test negative | Inpatient, and outpatient | ≥9 years | A(H1N1)pdm09 | 2012–13, 2013–14, 2015–16, 2017–18, and 2018–19 | 1, 3, and 5 |
| Martinez-Baz et al (2021)70 | Spain | Test negative | Inpatient | ≥9 years | A(H3N2) | 2011–12, 2013–14, 2014–15, 2016–17, 2017–18, and 2018–19 | 1, 3, and 5 |
| Martinez-Baz et al (2021)70 | Spain | Test negative | Outpatient | ≥9 years | A(H3N2) | 2011–12, 2013–14, 2014–15, 2015–16, 2016–17, 2017–18, and 2018–19 | 1, 3, and 5 |
| Martinez-Baz et al (2021)70 | Spain | Test negative | Inpatient and outpatient | ≥9 years | B | 2011–12, 2012–13, 2014–15, 2015–16, and 2017–18 | 1, 3, and 5 |
| Martinez-Baz et al (2021)71 | Spain | Test negative | Inpatient | 9–64 years | Any | 2013–14 to 2018–19 | 1 and 5 |
| Martinez-Baz et al (2021)71 | Spain | Test negative | Inpatient | ≥64 years | Any | 2013–14 to 2018–19 | 1 and 5 |
| McLean et al* (2014)22 | USA | Test negative | Outpatient | ≥9 years | A(H3N2) | 2004–05 to 2007–08 and 2010–11 to 2012–13 | 5 |
| McLean et al* (2014)22 | USA | Test negative | Outpatient | ≥9 years | A(H3N2) | 2004–05 to 2007–08, 2010–11 to 2012–13, 2007–08, and 2012–13 | 1 |
| McLean et al* (2014)22 | USA | Test negative | Outpatient | ≥9 years | B | 2004–05 to 2008–09 and 2010–11 to 2012–13 | 1 and 5 |
| McLean et al* (2015)72 | USA | Test negative | Outpatient | ≥9 years | A(H3N2), B/Yamagata | 2012–13 | 1 |
| McLean et al* (2017)73 | USA | Test negative | Outpatient | 2–17 years | A(H3N2) | 2014–15 | 1 |
| McLean et al† (2018)74 | USA | Test negative | Outpatient | 2–17 years | A(H1N1)pdm09 | 2013–14 and 2015–16 | 1, 2, and 3 |
| McLean et al† (2018)74 | USA | Test negative | Outpatient | 2–17 years | A(H3N2) | 2014–15 | 1, 2, and 3 |
| McLean et al† (2018)74 | USA | Test negative | Outpatient | 2–17 years | B/Victoria | 2014–15 and 2015–16 | 1 |
| McLean et al† (2018)74 | USA | Test negative | Outpatient | 2–17 years | B/Yamagata | 2013–14, 2014–15, and 2015–16 | 1 |
| McLean et al† (2018)74 | USA | Test negative | Outpatient | 2–17 years | B | 2013–14, 2014–15, and 2015–16 | 1, 2, and 3 |
| Mira-Iglesias et al (2018)75 | Spain | Test negative | Inpatient | ≥60 years | Any | 2016–17 | 2 |
| Mira-Iglesias et al (2019)76 | Spain | Test negative | Inpatient | ≥60 years | A(H1N1)pdm09, A(H3N2), and B/Yamagata | 2017–18 | 2 |
| Nichols et al† (2019)77 | Canada | Test negative | Inpatient | ≥16 years | A(H1N1)pdm09 | 2011–2012, 2012–13, and 2013–14 | 1 |
| Nichols et al† (2019)77 | Canada | Test negative | Inpatient | ≥16 years | A(H3N2) and B | 2011–12, 2012–13, 2013–14, and 2014–15 | 1 |
| Ohmit et al* (2014)13 | USA | Test negative | Outpatient | ≥9 years | A(H3N2) | 2011–12 | 1 |
| Ohmit et al (2015)78 | USA | Prospective cohort | Community | ≥9 years | Any | 2012–13 | 1 |
| Ohmit et al† (2016)79 | USA | Prospective cohort | Community | <9 years and ≥9 years | A(H1N1)pdm09 | 2013–14 | 1 |
| Ortqvist et al (2018)80 | Sweden | Retrospective cohort | Inpatient and outpatient | ≥66 years | Any | 2015–16 and 2016–17 | 1 |
| Ortqvist et al (2018)80 | Sweden | Retrospective cohort | Inpatient and outpatient | ≥70 years | Any | 2015–16 and 2016–17 | 4 and 5 |
| Pebody et al* (2013)81 | UK | Test negative | Outpatient | All | A(H1N1)pdm09 and B | 2010–11 | 1 |
| Pebody et al† (2017)82 | UK | Test negative | Outpatient | ≥18 years and 2–17 years | A(H3N2) | 2016–17 | 1 |
| Pebody et al* (2019)83 | UK | Test negative | Outpatient | ≥18 years and 2–17 years | A(H3N2), B | 2017–18 | 1 |
| Pebody et al* (2020)84 | England | Test negative | Inpatient | 2–17 years | A(H1N1)pdm09 and A(H1N1) | 2018–19 | 1 |
| Pebody et al* (2020)85 | England | Test negative | Inpatient | ≥65 years | A(H1N1)pdm09 and A(H1N1) | 2018–19 | 1 |
| Pebody et al (2020)86 | UK | Test negative | Outpatient | All ages | Any | 2018–19 | 1 |
| Petrie et al* (2016)87 | USA | Test negative | Inpatient | ≥18 years | A(H3N2) | 2014–15 | 1 |
| Petrie et al* (2017)88 | USA | Prospective cohort | Community | ≥9 years and 3–8 years | A(H3N2) and B/Yamagata | 2014–15 | 1 and 2 |
| Powell et al (2020)89 | USA | Test negative | Inpatient and outpatient | 6 months to 18 years | Any | 2017–18 | 1 |
| Rao et al (2021)90 | USA | Test negative | Outpatient | 6 months to 8 years | Any | 2016–17 and 2017–18 | 1 |
| Rondy et al* (2015)91 | Europe | Test negative | Inpatient | ≥18 years | A(H1N1)pdm09, A(H3N2), and B | 2012–13 | 1 |
| Rondy et al* (2017)92 | Europe | Test negative | Inpatient | ≥65 years | A(H3N2) | 2016–17 | 1 |
| Rondy et al (2017)93 | Europe | Test negative | Inpatient | ≥65 years | A(H1N1)pdm09 | 2012–13, 2013–14, and 2015–16 | 2 |
| Rondy et al (2017)93 | Europe | Test negative | Inpatient | ≥65 years | A(H3N2) | 2011–12 and 2013–14 | 2 |
| Rondy et al (2017)93 | Europe | Test negative | Inpatient | ≥65 years | B | 2012–13 and 2015–16 | 2 |
| Rose et al (2020)94 | Europe | Test negative | Inpatient | ≥65 years | A(H3N2) and B | 2017–18 | 2 |
| Saito et al (2017)95 | Japan | Test negative | Outpatient | ≥2 years | A | 2009–10, 2010–11, and 2011–12 | 1 |
| Saito et al (2018)96 | Japan | Test negative | Outpatient | 9–18 years | A and B | 2011–12, 2012–13, and 2013–14 | 1 and 3 |
| Shinjoh et al (2018)97 | Japan | Test negative | Outpatient | 2–15 years | Any and B | 2016–17 | 1 |
| Simpson et al (2015)98 | Scotland | Test negative | Outpatient | All ages | Any | 2000–01 to 2008–09 | 1 |
| Skowronski et al* (2012)99 | Canada | Test negative | Outpatient | ≥2 years | A(H1N1)pdm09 | 2010–11 | 1 |
| Skowronski et al* (2014)100 | Canada | Test negative | Outpatient | ≥2 years | A(H3N2), B, B/Victoria, and B/Yamagata | 2012–13 | 1 |
| Skowronski et al* (2014)101 | Canada | Test negative | Outpatient | ≥2 years | A(H1N1)pdm09, A(H3N2), B, B/Victoria, and B/Yamagata | 2011–12 | 1 |
| Skowronski et al* (2015)14 | Canada | Test negative | Outpatient | ≥2 years | A(H1N1)pdm09, B/Yamagata, and B | 2013–14 | 1 |
| Skowronski et al* (2016)18 | Canada | Test negative | Outpatient | ≥2 years and 20–64 years | A(H3N2), B, and B/Yamagata | 2014–15 | 1 |
| Skowronski et al* (2016)18 | Canada | Test negative | Outpatient | ≥3 years | A(H3N2), B, and B/Yamagata | 2014–15 | 2 |
| Skowronski et al† (2017)16 | Canada | Test negative | Outpatient | ≥9 years | A(H3N2) | 2010–11, 2012–13, and 2014–15 | 1 and 2 |
| Skowronski et al* (2017)17 | Canada | Test negative | Outpatient | ≥9 years | A(H1N1)pdm09, B, and B/Victoria | 2015–16 | 1 and 2 |
| Skowronski et al† (2019)102 | Canada | Test negative | Outpatient | ≥9 years | B/Yamagata | 2011–12, 2014–15, and 2017–18 | 1 |
| Skowronski et al* (2019)103 | Canada | Test negative | Outpatient | ≥9 years | A(H3N2) | 2018–19 | 1 |
| Skowronski et al* (2020)104 | Canada | Test negative | Outpatient | ≥9 years | A(H3N2) | 2016–17 and 2017–18 | 1 |
| Smithgall et al (2016)105 | USA | Test negative | Community | >6 months | Any | 2013–14 | 1 |
| Song et al* (2020)106 | China | Test negative | Inpatient and outpatient | ≥65 years | B | 2012–13, 2013–14, and 2014–15 | 1 |
| Sullivan et al (2013)15 | Australia | Test negative | Outpatient | ≥9 years | Any | 2011, 2012 | 1 |
| Sullivan et al† (2017)19 | Australia | Test negative | Outpatient | All ages | A(H3N2) and B | 2017 | 1 |
| Syrjänen et al (2014)107 | Finland | Prospective cohort | Community | 18–75 years | A(H1N1)pdm09 | 2010–11 | 1 |
| Thompson et al (2014)108 | USA | Test negative | Community | Not specified | A(H1N1)pdm09, A(H3N2), and B | 2010–11 and 2011–12 | 1 |
| Thompson et al* (2016)109 | USA | Test negative | Outpatient | 2–8 years | A(H3N2) | 2011–12 and 2012–13 | 1 |
| Thompson et al* (2016)109 | USA | Test negative | Outpatient | 2–8 years | B | 2012–13 | 1 |
| Valenciano et al (2016)110 | Europe | Test negative | Outpatient | ≥18 years | A(H1N1)pdm09, A(H3N2), and B | 2014–15 | 1 |
| Valenciano et al* (2018)23 | Europe | Test negative | Outpatient | ≥9 years | A(H1N1)pdm09 | 2012–13, 2013–14, 2014–15, and 2015–16 | 1 |
| Valenciano et al* (2018)23 | Europe | Test negative | Outpatient | ≥9 years | A(H3N2) | 2011–12, 2013–14, 2014–15, and 2016–17 | 1 |
| Valenciano et al* (2018)23 | Europe | Test negative | Outpatient | ≥9 years | B | 2012–13, 2014–15, and 2015–16 | 1 |
| Zhang et al (2017)111 | China | Case control | Community | 6–18 years | A | 2014–15 | 1 |
| Zhang et al* (2018)112 | China | Test negative | Outpatient | ≥2 years | A(H1N1)pdm09 and A(H3N2) | 2015–16 | 1 |
| Zhang et al* (2020)113 | China | Case control | Community | 6–19 years | A(H1N1)pdm09 and A(H3N2) | 2016–17 | 1 |
| Zimmerman et al* (2016)114 | USA | Test negative | Outpatient | ≥9 years | A(H3N2) and B/Yamagata | 2014–15 | 1 |
ROBINS-I=Risk of Bias in Non-Randomized Studies of Interventions.
*
Study was included in meta-analysis and was assessed as being at moderate risk of bias by the ROBINS-I.
†
Study was included in meta-analysis and was assessed as being at serious risk of bias by the ROBINS-I.