Modelling the impact of travel restrictions on COVID-19 cases in Newfoundland and Labrador

Imported infections disproportionally contribute to coronavirus disease 2019 (COVID-19) outbreaks in regions where infection prevalence is low. On May 4th, Newfoundland and Labrador implemented travel restrictions whereby non-residents could enter NL only with exemptions. As the prevalence of COVID-19 was low at the time, it is likely that the travel restrictions substantially reduced the COVID-19 epidemic in NL.  We fit a stochastic epidemic model to data describing the number of active COVID-19 cases in NL from March 14th – May 4th. We then forecast the distribution of outbreak sizes over the 9 weeks subsequent to May 4th, with and without the travel restrictions, and for physical distancing scenarios ranging from a 40% to 70% reduction in the daily contact rate relative to pre-pandemic levels. The implementation of travel restrictions in NL resulted in a 20-fold decrease in the number of cases over the subsequent 9 weeks. Assuming that physical distancing reduced the contact rate to 55% of its pre-pandemic level, the median number of cases without the travel restrictions was 19 and with the travel restrictions was 1. Using epidemic modelling, we show how the NL outbreak would have unfolded had travel restrictions not been implemented. The few COVID-19 cases reported following the implementation of travel restrictions is not evidence that the travel restrictions were unnecessary; rather our modelling shows that the travel restrictions are a plausible reason why there were few reported cases in NL in the 9-weeks after May 4th.

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