[13] Recommended framework of protocols for ensuring safe ship crew changes and travel during the coronavirus (COVID-19) pandemic http://www.imo.org/en/MediaCentre/HotTopics/Documents/COVID%20CL%204204%20adds/Circular%20Letter%20No.4204-Add.14%20-%20Coronavirus%20(Covid-19)%20-%20Recommended%20Framework%20Of%20Protocols.pdf
[28] WHO. Updated WHO recommendations for international traffic in relation to COVID-19 outbreak. https://www.who.int/news-room/articles-detail/updated-who-recommendations-for-international-traffic-in-relation-to-covid-19-outbreak