Table 1

Characteristics of the primary studies and LCI outcomes assessed

First author (year)	Location	World Bank country income group*	WHO region†	Study design	Time period	Pandemic or seasonal influenza	Reported LCI outcomes
First author (year)	Location	World Bank country income group*	WHO region†	Study design	Time period	Pandemic or seasonal influenza	LCI illness in ambulatory care settings	LCI hospitalisation	LCI ICU admission	LCI death
Ali (2016)34	Sindh Province, Pakistan	Lower-middle income	Eastern Mediterranean Region	Surveillance	October 2011 to June 2014	Seasonal	✔
Ampofo (2006)26	Salt Lake City, Utah, USA	High income	Region of the Americas	Retrospective cohort	July 2001 to June 2004	Seasonal		✔	✔	✔
Bennet (2016)43	Stockholm, Sweden	High income	European Region	Retrospective cohort	1998–1999 to 2013–2014	Pandemic H1N1 and seasonal		✔
Bhat (2005)7	USA	High income	Region of the Americas	Surveillance	September 2003 to May 2004	Seasonal				✔
Broor (2014)35	Haryana State, India	Lower-middle income	South-East Asia Region	Surveillance	August 2009 to July 2011	Pandemic H1N1 and seasonal		✔		✔
Budge (2014)37	Department of Cajamarca, Peru	Upper-middle income	Region of the Americas	Prospective cohort	May 2009 to September 2011	Pandemic H1N1 and seasonal	✔
Cohen (2016)38	Gauteng Province, KwaZulu-Natal Province, Mpumalanga Province, South Africa	Upper-middle income	African Region	Surveillance	January 2010 to December 2013	Seasonal		✔
Cox (2012)27‡	USA	High income	Region of the Americas	Surveillance (EIP)	April 2008 to April 2010	Pandemic H1N1 and seasonal		✔
Dawood (2010)28	USA	High income	Region of the Americas	Surveillance (EIP)	2003–2004 to 2007–2008	Seasonal		✔		✔
Griffin (2004)29§	Davidson County, Tennessee; Hamilton County, Ohio; and Monroe County, New York, USA	High income	Region of the Americas	Surveillance (NVSN)	2000–2001 to 2003–2004	Seasonal		✔
Grijalva (2006)30§	Davidson County, Tennessee, USA	High income	Region of the Americas	Surveillance (NVSN and EIP capture–recapture study)	2003–2004	Seasonal		✔
Grijalva (2007)31§	Davidson County, Tennessee; Hamilton County, Ohio; and Monroe County, New York, USA	High income	Region of the Americas	Surveillance (NVSN and EIP capture–recapture study)	2004–2005	Seasonal		✔
Iwane (2004)32§	Davidson County, Tennessee; Monroe County, New York; USA	High income	Region of the Americas	Surveillance (NVSN)	2000–2001	Seasonal		✔	✔
Ji (2010)39	Jiangsu province, China	Upper-middle income	Western Pacific Region	Surveillance	Jan 2007 to December 2008	Seasonal		✔	✔
Libster (2010)40	Buenos Aires, Argentina	Upper-middle income	Region of the Americas	Case series	May 2009 to July 2009	Pandemic H1N1		✔	✔	✔
Madhi (2014)16	Soweto, South Africa	Upper-middle income	African Region	RCT	2011 to 2012	Seasonal	✔	✔		✔
McMorrow (2015)36	Nairobi and Lwak, Kenya	Lower-middle income	African Region	Surveillance	January 2008 to December 2012	Pandemic H1N1 and seasonal		✔
Montes (2005)11	Regions of Basque Country, Spain	Upper-middle income	European Region	Retrospective cohort	July 2001 to June 2004	Seasonal		✔		✔
Nelson (2014)44	Hong Kong (China)	High income	Western Pacific Region	Retrospective cohort	April 2005 to March 2011	Pandemic H1N1 and seasonal		✔		✔
Poehling (2006)9§	Davidson County, Tennessee; Hamilton County, Ohio; and Monroe County, New York, USA	High income	Region of the Americas	Surveillance (NVSN)	2000–2001 to 2003–2004	Seasonal	✔	✔	✔
Poehling (2013)8§	Davidson County, Tennessee; Hamilton County, Ohio; and Monroe County, New York, USA	High income	Region of the Americas	Surveillance (NVSN)	2004–2005 to 2008–2009	Seasonal		✔
Proff (2009)33	Colorado, USA	High income	Region of the Americas	Surveillance	2004 to 2008 (1 October to 31 May annually)	Seasonal		✔
Silvennoinen (2011)45	Finland	High income	European Region	Retrospective cohort	July 1988 to June 2004	Seasonal		✔	✔
Stein (2010)46	Israel	High income	European Region	Prospective cohort	12 July 2009 to 24 December 2009	Pandemic H1N1		✔	✔
Tapia (2016)17	Bamako, Mali	Low income	African Region	RCT	12 September 2011 to 28 January 2014	Seasonal	✔	✔		✔
Yu (2014)41	Jingzhou City, Hubei Province, China	Upper-middle income	Western Pacific Region	Surveillance	April 2010 to April 2012	Seasonal		✔
Zhang (2016)42	Suzhou District, China	Upper-middle income	Western Pacific Region	Surveillance	April 2011 to March 2014	Seasonal	✔
Total=27 studies							6	23	7	9

*World Bank. World Development Indicators. Accessed: 10 January 2017. Available at: http://data.worldbank.org/data-catalog/world-development-indicators.
†WHO regional offices. Accessed: 10 January 2017. Available at: http://www.who.int/about/regions/en/.
‡Although the study objective was to report data from the 2009 H1N1 influenza pandemic, the reported incidence rates were from other years for comparison. As the incidence rates from 2008 to 2009 have not been reported elsewhere, they have been included.
§Surveillance was conducted from 1 November to 30 April each year, but the time period was extended if influenza was detected earlier or ended later.
EIP, Emerging Infections Program; ICU, intensive care unit; LCI, laboratory-confirmed influenza; NVSN, New Vaccine Surveillance Network; RCT, randomised controlled trial.