Lehmann 1991.

Methods	RCT of 12 months' duration, double‐blind, placebo‐controlled
Participants	Adults identified as suffering from chronic lung disease 62 participants included Setting: PNG highlands (under study surveillance) Recruitment: nominated Inclusion: productive cough fitting the time criteria for chronic lung disease Mean age of participants in the vaccine arm was 52.6 and in the placebo arm was 53.7
Interventions	Oral inactivated vaccine containing 10 Haemophilus influenzae Control: placebo, not specified Duration: 2 tablets in the morning for 3 consecutive days at monthly intervals for 3 consecutive months
Outcomes	Incidence of acute exacerbations Bacterial carriage Adverse side effects of NTHi vaccine
Notes	An acute exacerbation is defined as an increase in the volume and purulence of sputum with no evidence of respiratory distress, with or without chest pain or fever. This definition was consolidated with clinical examination, respiratory questionnaire in Melasian pigeon English, spirometry, and sputum samples Conducted at PNG Institute of Medical Research. Auspharm International Ltd cited in acknowledgements for setting up study and ongoing support
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	The investigators describe appropriate random sequence generation using a randomisation code for the courses of vaccine and placebo tablets
Allocation concealment (selection bias)	Low risk	Investigators enrolling participants could not foresee assignment, as randomisation was performed by the third party "Auspharm International Ltd." in New South Wales, Australia, accounting for the concealment of allocation
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Double‐blind trial. Blinding of participants and key study personnel ensured and unlikely that the blinding could have been broken
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Double‐blind trial. The outcomes assessed in both groups were measured using the same questionnaire and a medical examination. Methods of ensuring blinding of outcome assessment were not reported
Incomplete outcome data (attrition bias) All outcomes	High risk	Concluded from the trial report, there is no mention of ITT for participants lost to follow‐up (8 from vaccine group and 3 from placebo group). This is substantial considering the small group sizes; it is possible that it had an effect on the outcome
Selective reporting (reporting bias)	Low risk	Study report fails to include results for a key outcome (prescription rate of antibiotics) that would be expected to have been reported for such a study, although the protocol is not available. However, all primary outcomes are reported
Other bias	Low risk	The study appears to be free of other sources of bias