pca Black 2004.

Methods	Retrospective cohort study assessing the effectiveness of flu vaccination for the prevention of ILI or pneumonia in pregnant women and their newborns
Participants	All women with live births in Kaiser Permanente Northern California (KPNC) between the November and February of 5 subsequent seasons (1997 to 1998 to 2001 to 2002, n = 49,585), excluding cases lacking birth date information and women who were discharged after the end of the flu season. All live births in KPNC that occurred during the same time periods as for the mothers (n = 48,639), again cases lacking gestational age or gender information and infants discharged after the end of the flu season were excluded.
Interventions	Immunisation with flu vaccine (no details about type and composition). Data about immunisation were obtained from the KPNC database. In all, 3707 out of the 49,585 pregnant women included in the study were vaccinated, whereas this was 3652 out of the 48,639 live births.
Outcomes	Hospitalisation for pneumonia or influenza: at least 1 inpatient stay during the same flu season as delivery or birth with a principal (first) diagnosis of either influenza or pneumonia. To identify these outcomes, the following ICD (9th revision) codes were used to identify inpatient cases: influenza 487 and pneumonia 480, 481, 482, 483, 484, 485, and 486. Outpatient visits: at least 1 physician visit during the same flu season as delivery or birth with 1 of the following diagnoses: upper respiratory infection, pharyngitis, otitis media, asthma, bronchial asthma, viral infection, pneumonia, fever, cough or wheezing associated with respiratory illness. This information was available from the KPNC databases, which include laboratory, hospitalisation, and outpatient utilisation information for their members. The effect measure (hazard ratio and corresponding 95% confidence interval) was calculated for ILI visits (including and excluding asthma diagnoses) for the mother and hospitalisation for pneumonia or influenza, ILI visits (excluding otitis media), and otitis media visits in newborns. Caesarean section. Preterm delivery (< 37 weeks).
Notes	Government‐funded
Risk of bias
Bias	Authors' judgement	Support for judgement
PCS/RCS ‐ selection exposed cohort All outcomes	Unclear risk	From KPNC databases: the influenza vaccination status of women in the cohort was determined through review of the Kaiser Immunization Tracking System database.
PCS/RCS ‐ selection non‐exposed cohort All outcomes	Unclear risk	From KPNC databases
PCS/RCS ‐ comparability All outcomes	High risk	No matching
PCS/RCS ‐ assessment of outcome All outcomes	Unclear risk	KPNC maintains administrative databases that include laboratory, hospitalisation, and outpatient utilisation information for their members.
Summary assessment	High risk	High