Data collection methods used in 2012 have been described previously.13 A random sample of 1142 adult women who gave birth to a live baby between 07/04/2013 and 06/10/ 2013 (i.e were pregnant during 2013 influenza vaccination season) was selected from the WA Midwives’ Notification System, a statutory database of attended births. As the total sample size in 2013 was doubled from 2012, it was not necessary to oversample women from country areas in order to make comparisons between metropolitan and country uptake. The sample size provides a maximum relative standard error of 3.5% at the standard 95% confidence interval.