pca Hulka 1964.

Methods	Prospective cohort study assessing the effectiveness of flu vaccination in pregnancy
Participants	Pregnant women (n = 544) recruited from the "hill" district of Pittsburgh
Interventions	Polyvalent flu vaccine containing 200 units of A2 antigen Placebo Two 1 mL doses were administered 1 month apart.
Outcomes	Adverse effects following immunisation (pain, malaise) ILI Days in bed Assessed by means of questionnaires/phone interviews after epidemic
Notes	Effectiveness follow‐up was available for 59% and 100% of participants in the intervention and placebo arm, respectively. Funding source ‐ mixed
Risk of bias
Bias	Authors' judgement	Support for judgement
PCS/RCS ‐ selection exposed cohort All outcomes	High risk	Unclear
PCS/RCS ‐ selection non‐exposed cohort All outcomes	High risk	Unclear
PCS/RCS ‐ comparability All outcomes	High risk	Unclear ‐ high attrition
PCS/RCS ‐ assessment of outcome All outcomes	High risk	Interview
Summary assessment	High risk	Unclear