- Correspondence to Dr Janneke C M Heijne, Centre for Infectious Diseases Control, National Institute for Public Health and the Environment (RIVM), P.O. Box 1, 3720 BA Bilthoven, The Netherlands;
- Received November 20, 2017
- Revised May 9, 2018
- Accepted May 13, 2018
- First published June 20, 2018.
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