“…This was a particular issue for vaccine or drug trials, but not for observational studies. Safety concerns were mentioned in 45 papers [1, 20-23, 26, 28, 30-32, 34, 36, 37, 39-42, 45, 47, 48, 50-53, 55, 56, 58, 59, 61, 62, 67-69, 71, 76, 77, 88, 92-99], ranked in the top three reasons 32 times [1, 20, 21, 23, 30-32, 36, 37, 40, 41, 45, 47, 48, 50-53, 55, 56, 58, 61, 65, 67-69, 71, 77, 93, 94, 96-98], and identified as the top reason for non-participation 16 times [31,32,40,45,47,48,55,58,61,65,68,71,77,93,94,96,98]. Safety concerns were consistently ranked as most important in all categories, with the exception of North Africa and the Middle East, where they ranked second.…”