evidence: Opinion: With the death toll rising in Samoa's measles epidemic, vaccinologist Dr Helen Petousis-Harris explores why Samoa's immunity is so low and how bad the epidemic could get. Samoa are experiencing a devastating measles epidemic. It is possible that 2-3% of the population will ultimately be infected by the time it is over. Hopefully the mass immunisation campaign currently under way can mitigate some of this; for many it is too late. [...] The general answer is simple. Samoa has long term low immunisation coverage—some of the lowest vaccination rates in the world. This low immunisation coverage has left Samoa extremely vulnerable to measles—a lit match to dry tinder and gasoline. With the global resurgence of measles, the risk of an importation to this vulnerable community was almost inevitable.