Objectives: Describe and compare the proportion of studies reporting the method used to assign study units to treatment groups, reporting a random allocation approach, reporting 18 REFLECT items, and the proportion of studies having a low risk-of-bias assessment in swine vaccination trial studies published after the REFLECT statement, compared to studies published before.

Materials and Methods: The study population was 61 studies that evaluated vaccines targeted at pathogens affecting swine health or pork safety. Two reviewers assessed the reporting of 18 of 22 REFLECT items and 5 risk-of-bias domains.

Results: Authors reported the method used to allocate experimental units in 33 of 42 (79%) and 14 of 19 (74%) studies published prior to and following REFLECT, respectively. There has been a substantial shift in the reporting of allocation approaches. Before 2011, only 2 of 25 (8%) studies that reported using random allocation provided supporting evidence. This increased in studies published between 2011-2017 (4 of 6; 66%). Before 2011, 8 of 33 (24%) studies reported using systematic allocation, which increased to 43% (6 of 14 studies) between 2011-2017. There has also been an increase in the prevalence of reporting for 14 of the 18 REFLECT items. There was an increase in the number of studies reporting evidence to support true randomization to group and data that suggests few baseline imbalances.

Implications: Data from this study suggests swine vaccination trial reporting improved, which may be due to researchers having more access to better quality information.