Figure 3

a – d. Mean rates of secondary outbreak cases per primary case. Mean (and 95% confidence intervals) rates of secondary outbreak cases per primary case, by a) country, b) median age, c) mode of primary transmission and d) mode of secondary transmission shown on log (1+x) scales. For 3a 'other' encompasses outbreaks from Scandinavia and Ireland, and for 3b the 'unknown' category encompasses outbreaks where the median age is not known.