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

Hurford, A.; Rahman, P.; Loredo-Osti, J. C.

BACKGROUND: In many jurisdictions public health authorities have implemented travel restrictions to reduce coronavirus disease 2019 (COVID-19) spread. Previous research has considered the impact of international travel restrictions on COVID-19 dynamics, but in response to the pandemic, policies that restrict travel within countries have also been implemented, and the impact of these restrictions is less well studied. On May 4th, 2020, Newfoundland and Labrador (NL) implemented travel restrictions such that non-residents were required to have exemptions to enter the province. METHODS: 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 predicted possible outbreaks 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. RESULTS: We find that the mean number of clinical COVID-19 cases would have been 12.4 times higher without the travel restrictions. Furthermore, without the travel restrictions there is a substantial risk of very large outbreaks. INTERPRETATION: Using epidemic modelling, we show how the NL COVID-19 outbreak could have unfolded had the travel restrictions not been implemented. Both physical distancing and travel restrictions affect the local dynamics of the epidemic. Our modelling shows that the travel restrictions are a plausible reason why there were so few reported COVID-19 cases in NL in the 9 weeks after May 4th.