Earle 2003.

Methods	Retrospective, observational cohort study Location: USA, Boston
Participants	Stage 4 colorectal adenocarcinoma, with active chemotherapy treatment 1225 adults, 1577 person‐years: 626 person‐years vaccinated, 951 person‐years unvaccinated Mean age 74 year in both groups
Interventions	Yearly influenza vaccination, examined through medical bills
Outcomes	Adjusted all‐cause mortality Confirmed influenza Pneumonia Hospitalisation duration Chemotherapy interruptions Influenza‐related mortality Mean number of hospital days
Notes	Results given per person‐years
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	High risk	Non‐random
Allocation concealment (selection bias)	High risk	Non‐random
Incomplete outcome data (attrition bias) All outcomes	High risk	Mortality data were given only for 697 of 1054 patients.
Selective reporting (reporting bias)	Low risk	None identified
Other bias	High risk	No control for cancer stage and functional capacity, no sample size calculation, funding not mentioned.
Blinding of participants and personnel (performance bias) All outcomes	High risk	Non‐blinded
Blinding of outcome assessment (detection bias) All outcomes	High risk	Non‐blinded