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

Al Wahaibi, Adil; Al Manji, Abdullah; Al Maani, Amal; Al Rawahi, Bader; Al Harthy, Khalid; Alyaquobi, Fatma; Al-Jardani, Amina; Petersen, Eskild; Al-Abri, Seif

BACKGROUND: COVID-19’s emergence carries with it many uncertainties and challenges, one of which is epidemic management strategies. Oman has implemented non-pharmaceutical interventions (NPIs) to mitigate the impact of COVID-19. However, responses to NPIs may be different across different populations in a country with a large number of migrants like Oman. This study investigates the different responses to NPIs assessing the use of time-varying reproduction number (R(t)) to monitor it. METHODS: Polymerase chain reaction (PCR) laboratory-confirmed COVID-19 data from Oman was used from February 24th to June 3rd, 2020 and included 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, we identified 2769 infector–infectee pairs to calculate R(t). There was a sharp drop in R(t) from 3·7, (95% confidence interval [CI] 2·8-4·6) mid-March to 1·4 (95% CI 1·2–1·7) in late March in response to NPIs. Then R(t) decreased to 1·2 (95% CI 1·1–1·3) late April when it rose, corresponding to the easing up of NPIs. Comparing the two groups, the response to major public health controls was more evident in Omanis in reducing the R(t) to 1·09 (95% CI 0·84–1·3) at the end of March. INTERPRETATION: Use of real-time estimation of R(t) has allowed us to follow the effect of NPIs. The migrant population responds differently than the Omani population.