MW, one of the safer destinations you could visit, it's pretty laid back. Sunburn and a kava hangover might be your biggest worries. Obviously petty crime does exist so don't be careless with your valuables. Women should be careful about where they walk at night if they're alone - avoid dark streets and near bars - the usual stuff anywhere in the world.
More detail here: http://journals.worldnomads.com/safetyhub/story/75744/Vanuatu/Vanuatu-Travel-Tips-and-Safety-Guide
Phil from the safety hub over 5 years ago