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Table 2 General properties of the studies

From: One “misunderstood” health issue: demonstrating and communicating the safety of influenza a vaccination in pregnancy: a systematic review and meta-analysis

Studies No of women vaccinated (n) No of women unvaccinated (n) Type of study Bias risk grade
Baum2015 [15] 34,241 9363 Cohort study B
Beau2014 [16] 1645 3290 Cohort study B
Chambers2013 [17] 841 191 Cohort study B
Chambers 2016 [18] 1263 467 Cohort study B
Cleary2014 [19] 2996 3898 Cohort study B
Fabiani2015 [20] 2003 98,329 Cohort study B
Fell2012 [21] 23,340 32,230 Cohort study B
Kallen2012 [22] 18,612 83,298 Cohort study B
Legge2014 [23] 1958 10,265 Cohort study B
Lin2012 [24] 198 198 Cohort study B
Maas2015 [25] 1357 669 Cross sectional linkage study B
Olsen2016 [26] 2172 2931 Cohort study B
Pasternak2012 [27] 345 + 6644 22,917 + 46,443 Cohort study B
Richards2013 [28] 1125 1545 Cohort study B
Rubinstein2013 [29] 7293 23,195 Cross sectional study B
Sheffield2012 [30] 8690 76,153 Cohort study B
Steinhoff2012 [31] 161 166 Randomized trial B
Steinhoff2017 [32] 1847 1846 Randomized trial B
Zerbo2017 [33] 64,748 81,119 Cohort study B
Total no of participants (n) 181,479 498,513