Trends in SARS-CoV-2 Reproduction Number Following Different Restrictions

Dawn O'Shea

October 30, 2020

The effects of introducing and lifting COVID-19 safety restrictions are delayed by one to three weeks, with this delay being longer when lifting restrictions, according to a study led by the University of Edinburgh published in  Lancet Infectious Diseases.

In the modelling study, data on daily country-level estimates of the reproduction number (R) from the London School of Hygiene & Tropical Medicine was linked with data on country-specific policies on NPIs from the Oxford COVID-19 Government Response Tracker, available between 1 January 2020 and 20 July 2020. A total of 131 countries were included in the analysis.

A decreasing trend over time in R ratio (RR) followed the introduction of school closure, workplace closure, public events ban, requirements to stay at home and internal movement limits. The reduction in R ranged from 3 to 24 per cent on day 28, however, the reduction was significant only for public events ban (RR, 0.76).

An increasing trend over time in the RR was found following the relaxation of school closure, bans on public events, bans on public gatherings of >10 people, requirements to stay at home and internal movement limits. The increase in R ranged from 11 to 25 per cent on day 28 but was significant only for school reopening (RR, 1.24) and lifting bans on public gatherings (RR, 1.25).

It took a median of eight days following the introduction of an NPI to observe a 60 per cent of the maximum reduction in R and 17 days (14-20) following relaxation to observe a 60 per cent of the maximum increase in R.

A control strategy of banning public events and public gatherings of >10 people was estimated to reduce R, with an RR of 0.71 on day 28, decreasing to 0.62 if measures to close workplaces were added; 0.58 if measures to close workplaces and internal movement restrictions were added; and 0.48 if measures to close workplaces, internal movement restrictions and requirements to stay at home were added.

Li Y, Campbell H, Kulkarni D, Harpur A, Nundy M, Wang X, Nair H; Usher Network for COVID-19 Evidence Reviews (UNCOVER) group. The temporal association of introducing and lifting non-pharmaceutical interventions with the time-varying reproduction number (R) of SARS-CoV-2: a modelling study across 131 countries. Lancet Infect Dis. 2020 Oct 22 [Epub ahead of print]. doi: 10.1016/S1473-3099(20)30785-4 View full text

This article originally appeared on Univadis, part of the Medscape Professional Network.

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