Acknowledgements

This unit was written by Basiro Davey, Carol Midgley, Claire Rostron and Daniel Berwick.

Except for third party materials and otherwise stated in the acknowledgements section, this content is made available under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 Licence [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] .

The material acknowledged below is Proprietary and used under licence (not subject to Creative Commons Licence). Grateful acknowledgement is made to the following sources for permission to reproduce material in this unit:

Figure 8: Chris Knapton/Science Photo Library/Universal Images Group

Figure 12: Saturn Stills/Science Photo Library/Universal Images Group

Figure 14: The Global Polio Eradication Initiative © Copyright 2010

Every effort has been made to contact copyright owners. If any have been inadvertently overlooked, the publishers will be pleased to make the necessary arrangements at the first opportunity.

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