  This paper develops an easily-implementable version of Page's CUSUM
quickest-detection test, designed to work in certain composite hypothesis
scenarios with time-varying data statistics. The decision statistic can be cast
in a recursive form and is particularly suited for on-line analysis. By
back-testing our approach on publicly-available COVID-19 data we find reliable
early warning of infection flare-ups, in fact sufficiently early that the tool
may be of use to decision-makers on the timing of restrictive measures that may
in the future need to be taken.
