Date	Event	Description
31 December 2016	New search has been performed	For this update we included 20 new trials (aa Mcbride 2016a; aa Mcbride 2016b; aa Treanor 2011; bb Dauvilliers 2013; bb MacIntyre 2013; bb Rouleau 2014; cb O'Flanagan 2014; cb Persson 2014; paa Ma 2014; paa Madhi 2014; pca Ahrens 2014; pcb Beau 2014; pcb Cantu 2013; pcb Chambers 2013; pcb Cleary 2014; pcb Dodds 2012; pcb Louik 2013; pcb Ludvigsson 2013; pcb Nordin 2014; pcb Rubinstein 2013; pcb Trotta 2014). We excluded 21 new trials (Andersson 2015; Atsmon 2012; Baxter 2013; Chavant 2013; Chichester 2012; Couch 2012; Duffy 2014; Greene 2013; Heinonen 1973; Huang 2011; Lavallee 2014; Lind 2014; Liu 2012; Montplaisir 2014; Phonrat 2013; Pleguezuelos 2012; Scheifele 2013; Sipilä 2015; Taylor 2012; Thompson 2014; Warren‐Gash 2013). We excluded 17 trials previously awaiting classification (ab López‐Macías 2011a; ab López‐Macías 2011b; ab Mallory 2010; ab Plennevaux 2010; ab Precioso 2011; ab Treanor 2010; ab Turley 2011; ab Wacheck 2010; Atsmon 2012; Chichester 2012; Couch 2012; Heinonen 1973; Huang 2011; Phonrat 2013; Pleguezuelos 2012; Scheifele 2013; Taylor 2012; Xu 2012).
31 December 2016	New citation required but conclusions have not changed	Our conclusions remain unchanged.
15 September 2014	Feedback has been incorporated	Feedback comment submitted.
4 March 2014	New search has been performed	We updated the searches and included 41 new trials (aa Barrett 2011; aa Frey 2010; aa Jackson 2010a; aa Jackson 2010b; aa Langley 2011; aa Monto 2009; aa Ohmit 2006; aa Ohmit 2008; bb Dieleman 2011a; bb Dieleman 2011b; bb Dieleman 2011c; bb Dieleman 2011d; bb Dieleman 2011e; bb Galeotti 2013; bb Garbe 2012; bb Grimaldi‐Bensouda 2011; bb Grimaldi‐Bensouda 2012; bb Hernan 2004; bb Ray 2011; bb Zorzon 2003; cb Bardage 2011; cb Baxter 2012; cb Moro 2013; cb Ray 2011; pba Benowitz 2010; pba Poehling 2011; pbb Irving 2013; pca Black 2004; pca Eick 2011; pca France 2006; pca Hulka 1964; pca Munoz 2005; pca Yamada 2012; pcb Deinard 1981; pcb Fell 2012; pcb Håberg 2013; pcb Heikkinen 2012; pcb Källén 2012; pcb Launay 2012; pcb Lin 2012; pcb Nordin 2013; pcb Omer 2011; pcb Oppermann 2012; pcb Pasternak 2012; pcb Richards 2013; pcb Sheffield 2012; pcb Toback 2012), which corresponded to 47 data sets. We excluded 63 new trials.
4 March 2014	New citation required and conclusions have changed	For this update we added vaccine efficacy/effectiveness and safety evidence on pregnant women.
24 May 2013	Feedback has been incorporated	Feedback comment added to the review.
15 June 2010	New citation required but conclusions have not changed	For this update Eliana Ferroni (EF), Lubna Al Ansary, and Ghada Bawazeer joined as new authors. Carlo Di Pietrantonj (CDP), Alessandro Rivetti (AR), and Tom Jefferson (TJ) remained.
15 June 2010	New search has been performed	Searches conducted. For this update we screened 3729 titles and identified 44 studies for possible inclusion. We included two new trials, aa Beran 2009a and aa Beran 2009b, and excluded three new trials (Belongia 2009; Chou 2007; Khazeni 2009).
10 May 2009	Amended	Contact details updated.
26 April 2008	Amended	Converted to new review format.
15 April 2007	Feedback has been incorporated	Feedback comment added to review.
16 February 2007	New citation required and conclusions have changed	Substantive amendment. For the 2006 update we included 30 new studies but tightened up our inclusion criteria, excluding studies with influenza B vaccine as a control, which did not come within our comparator rules of placebo or do nothing. Twenty‐two of the new included studies were clinical trials evaluating the efficacy or safety (or both) of different type of influenza vaccines. We also carried out a subanalysis of the five 1968 to 1969 pandemic trials (with numerous subtrials) in our data set. Finally, we included more data (10 studies) on potential serious or rare harms, looking also at non‐randomised evidence.
4 April 2006	Feedback has been incorporated	Feedback comment added to review.
24 May 2004	New search has been performed	Searches conducted. In the 2004 update we included five more studies not identified by the original searches and updated the text and references. We also assessed and excluded 25 more studies. We used the random‐effects model for analysing all the comparisons and outcomes. The updated results and conclusions of our review did not change significantly much.
6 July 1997	New search has been performed	Searches conducted. Review first published Issue 4, 1999.