Carbon emissions of a vaccine trial implemented in Uganda: retrospective assessment to identify actions to enhance researchers' environmental responsibilities.

OBJECTIVES: To estimate the carbon footprint of a vaccine trial conducted in Uganda and to identify opportunities to reduce greenhouse gas emissions in future trials.

DESIGN: Retrospective carbon footprint assessment of all trial-related activities conducted in Uganda (ClinicalTrials.gov ID NCT02991495), following the Greenhouse Gas Protocol and the guidance provided by the Low Carbon Clinical Trials Group.

SETTING: The activities related to the yellow fever vaccine fractional dose trial implemented in Mbarara, with contributions from international collaborators.

PARTICIPANTS: The study assessed processes; no participants have been included.

METHODS: Trial activities were retrospectively quantified and converted into a greenhouse gas estimate using publicly available emission factors. The boundaries of the study were defined to cover the set-up, implementation and close-out phases. Emissions were categorised by source, including personnel, travel, medical supply and laboratory.

RESULTS: The vaccine trial produced an estimated 224.66 tonnes of carbon dioxide equivalent (tCOe). The largest emission category was related to the research centres, accounting for 78.80 tCOe (35.07%), with the Mbarara research centre representing 75.74 tCOe (32.38%), including commuting (21.01 tCOe), waste disposal (19.31 tCOe), goods and services (18.66 tCOe) and energy (13.75 tCOe). International travel, including air, non-air travel and accommodation accounted for 59.37 tonnes COe (26.43%), with the majority attributed to air travel (53.60 COe). Additional contributors included road travel by trial team and participants' travel to attend trial's visits. The storage of samples at -80°C in ultra-dry freezers was not a significant contributor due to the low volume of samples stored. However, important differences were observed in sample storage emissions between settings that relied more heavily on oil-based electricity and those with greater dependence on hydroelectric power.

DISCUSSION: This study highlights multiple opportunities to reduce the carbon emissions of clinical trials. These include already recognised actions such as higher use of solar energy and reduction of international travel. Nevertheless, to improve sustainability of trials, attention should be given to all controllable processes across the trial lifecycle and not solely to the main drivers of emissions. For this, environmental considerations should be present from the initial trial conception phase, involving for instance decisions about the number of trial visits and where these are conducted and taking rational decisions about the long-term storage of samples.

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