pca Eick 2011.

Methods	Prospective cohort study carried out in 6 hospitals located in the Navajo and White Mountain Apache reservation during 3 subsequent epidemic seasons (2002 to 2005)
Participants	Mother‐infant pairs recruited after delivery at Indian Health Service hospitals on the Navajo or White Mountain Apache reservation, either at the hospital or by home visit. The study was conducted during 3 influenza seasons from November 2002 to September 2005. The enrolment periods for each year were: 1 December 2002 to 15 March 2003; 1 November 2003 to 8 March 2004; 1 November 2004 to 15 March 2005. Inclusion was restricted to mothers who delivered a healthy infant at 36 weeks or later gestation during the enrolment periods. Eligible infants were aged 2 weeks or younger at enrolment. Overall, 1169 mother‐infant pairs were enrolled in the study (241 in 2002 to 2003; 574 in 2003 to 2004; and 354 in 2004 to 2005). Of these, 1160 had at least 1 serum sample and were included.
Interventions	Immunisation of the mother with influenza vaccine. Assessed by reviewing of medical record (also in order to obtain information about prenatal visits, illnesses, and birth information, in addition to administration and timing of influenza vaccine) or, if missing, by maternal report at enrolment. The decision for influenza vaccination was made by the treating clinician and the pregnant woman; personnel had no role in this decision. Altogether 587 children were born from an unvaccinated mother and 573 from a vaccinated mother during the 3 study seasons.
Outcomes	Surveillance for all medically attended illnesses in enrolled infants was conducted at Indian Health Service and nearby private facilities through the influenza season, or until the child reached 6 months of age (whichever came first). It also included review of the clinic, emergency department, and inpatient paediatric ward logs. A nasopharyngeal aspirate specimen for viral culture was obtained from infants with ILI within 72 hours of the medical visit. Medically attended ILI: defined as a medical visit with at least 1 of the following signs or symptoms reported: fever of 38.0 ºC or higher, diarrhoea, or respiratory symptoms (including cough, runny nose, or difficulty breathing). Laboratory‐confirmed influenza: the first ILI episode with either: isolation of influenza virus from the nasopharyngeal aspirate specimen; a 4‐fold or greater rise in HI antibody in serum collected at 2 to 3 or 6 months compared with the previous serum specimen, indicating influenza virus infection during the time interval; or a positive rapid influenza diagnostic test result with a medical diagnosis of influenza.
Notes	Funding/support: "The study was funded by the National Vaccine Program Office, Department of Health and Human Services, the Office of Minority Women’s Health, Centers for Disease Control and Prevention, Aventis‐Pasteur, and Evans‐Powderject." Funding source ‐ mixed
Risk of bias
Bias	Authors' judgement	Support for judgement
PCS/RCS ‐ selection exposed cohort All outcomes	Unclear risk	The study was carried out within Indian reservations.
PCS/RCS ‐ selection non‐exposed cohort All outcomes	Low risk	Derived from the same community as the exposed cohort
PCS/RCS ‐ comparability All outcomes	Unclear risk	Reported for some parameters only: sex, presence of household smokers, having wood or coal stove in the house (more frequent among vaccinated), presence of other children in day care, infant breast fed (more frequent among vaccinated), gestational age, mean birth weight
PCS/RCS ‐ assessment of outcome All outcomes	Low risk	Active surveillance and testing for laboratory confirmation for symptomatic ILI cases
Summary assessment	Unclear risk	Unclear