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Vallance AE, Fearnhead NS, Kuryba A, Hill J, Maxwell-Armstrong C, Braun M, van der Meulen J, Walker K.Vallance AE, et al.BMJ. 2018 May 2;361:k1581. doi: 10.1136/bmj.k1581.BMJ. 2018.PMID: 29720371Free PMC article.