COVID-19 epidemic monitoring after non-pharmaceutical interventions: The use of time-varying reproduction number in a country with a large migrant population

Background: COVID-19's emergence carries with it many uncertainties and challenges, including strategies to manage the epidemic. Oman has implemented non-pharmaceutical interventions (NPIs) to mitigate the impact of COVID-19. However, responses to NPIs may be different across different populations within a country with a large number of migrants, such as Oman. This study investigated the different responses to NPIs, and assessed the use of the time-varying reproduction number (R_t) to monitor them.

Methods: Polymerase chain reaction (PCR) laboratory-confirmed COVID-19 data for Oman, from February 24 to June 3, 2020, were used alongside demographic and epidemiological information. Data were arranged into pairs of infector-infectee, and two main libraries of R software were used to estimate reproductive number (R_t). R_t was calculated for both Omanis and non-Omanis.

Findings: A total of 13,538 cases were included, 44.9% of which were Omanis. Among all these cases we identified 2769 infector-infectee pairs for calculating R_t. There was a sharp drop in R_t from 3.7 (95% confidence interval [CI] 2.8-4.6) in mid-March to 1.4 (95% CI 1.2-1.7) in late March in response to NPIs. R_t then decreased further to 1.2 (95% CI 1.1-1.3) in late April after which it rose, corresponding to the easing of NPIs. Comparing the two groups, the response to major public health controls was more evident in Omanis in reducing R_t to 1.09 (95% CI 0.84-1.3) by the end of March.

Interpretation: Use of real-time estimation of R_t allowed us to follow the effects of NPIs. The migrant population responded differently than the Omani population.