  During 2014-15, there were several outbreaks of nominated-based online social
contagion. These infections, which were transmitted from one individual to
another via posts on social media, included games such as 'neknomination', 'ice
bucket challenge', 'no make up selfies', and Facebook users re-posting their
first profile pictures. Fitting a mathematical model of infectious disease
transmission to outbreaks of these four games in the United Kingdom, I
estimated the basic reproduction number, $R_0$, and generation time of each
infection. Median estimates for $R_0$ ranged from 1.9-2.5 across the four
outbreaks, and the estimated generation times were between 1.0 and 2.0 days.
Tests using out-of-sample data from Australia suggested that the model had
reasonable predictive power, with $R^2$ values between 0.52-0.70 across the
four Australian datasets. Further, the relatively low basic reproduction
numbers for the infections suggests that only 48-60% of index cases in
nomination-based games may subsequently generate major outbreaks.
