/seasonal_onset.html">seasonal_onset()</a></code> function. Here, a window size of
<code>k=5</code> is specified, meaning that a total of 5 weeks is used
in the local estimate of the exponential growth rate.
<code>na_fraction_allowed = 0.4</code> defines how large a fraction of
cases in the <code>k</code> window that are allowed to be
<code>NA</code>, here <code>0.4*5 = 2</code> cases. Additionally, a 95%
confidence interval is specified. Finally, the exponential growth rate
is estimated using quasi-Poisson