The gradual release exit strategy after lockdown against COVID-19.

Since the first case report from Wuhan, the COVID-19 pandemic has spread with unprecedented speed and scale globally to more than 188 countries and regions. Over 10 million cases and 500,000 deaths have been reported worldwide by the end of June 2020. However, case numbers in countries and regions in Asia remain comparatively low although they were the first to report case importation in January: Thailand on 13 Jan, Japan on 15 Jan, South Korea on 20 Jan, Hong Kong and Taiwan on 22 Jan, Macau, Singapore and Vietnam on 23 Jan, Nepal on 24 Jan and Malaysia on 25 Jan [1]. Different non-pharmaceutical interventions have been implemented depending on the local situations, including physical distancing, school and workplace closure, rapid contact tracing and testing, targeted or nationwide lockdown etc. As these Asian countries and regions start relaxing the interventions gradually, their experiences are worth examining so that other countries may incorporate those insights into their own pandemic control strategies.

Seeded by infected overseas returnees and migrant workers, Singapore experienced a local outbreak in March-April and announced one-month lockdown on 3 April which was later extended to 1 June. On 2 June, Singapore started to lift the lockdown in three phases. In The Lancet Regional Health-Western Pacific, Dickens and colleagues explore the potential impact of a gradual release exit strategy (GRES) in the context of lockdown and social distancing in Singapore, which allows immediate reopening of schools but gradual easing of workplace distancing [2]. Their work is based on an agent-based epidemic model parameterized by detailed data of the Singaporean population published earlier to assess the effects of combined interventions against the COVID-19 pandemic [3]. In the post-lockdown period simulated by the model, GRES averts a substantial proportion of cases compared with no exit strategy (i.e. immediate returning to pre-epidemic state for all schools, workplaces and the community) whilst simultaneously reduces the epidemic peak size and thus the stress on the healthcare system. At the time of writing, it appears the actual reopening strategy, which is similar to GRES, has so far been successful at avoiding resurgence of case number in Singapore since the lockdown was lifted on 2 June.

As the first country to report COVID-19 detection outside China, Thailand issued a nationwide curfew (i.e. banning all people from leaving their homes from 10 pm to 4 am) on 3 April in response to the rapid increase of local cases in late March. The curfew was gradually lifted on 1 June and officially ended on 15 June with no local cases (for 21 days) since then. Similarly, after the nationwide lockdown between 1 and 15 April, Vietnam managed to reopen its economy gradually. Although targeted lockdown was extended to late April in 28 out of 63 provinces, Vietnam successfully kept the case number low and death count at zero [1]. Without explicitly elaborating their reopening plan, Vietnam brought its manufacturing sector back to growth again in June after the first five months’ decline in 2020 [4]. Successful control of the pandemic in both countries has been attributable to several key factors, including rapid responses, proactive containment strategies, comprehensive tracing and testing, effective communication, and well-developed public health systems [5,6].

The design of gradual release exit strategy depends on knowledge of the local transmission dynamics of COVID-19. GRES assumed immediate reopening of schools by adopting Singapore's actual practice, but the effects of school closure and reopening remain unclear. Uniform susceptibility was assumed across all age groups in GRES but recent studies suggested children and adolescents were less susceptible than adults [7,8]. Additionally, the effects of GRES were also sensitive to the assumption about the proportion of asymptomatic and pre-symptomatic infections, which subsequently affects the effectiveness of contact tracing and isolation. Due to the absence of sustained community outbreaks in Singapore, the authors did not attempt to calibrate the model with observed case data but parameterized it with assumed parameters such as R0 = 2. The model would need to be updated dynamically over time by fitting more parameters to local observed data within Singapore after the lockdown is lifted.

In the absence of safe and effective vaccines, premature relaxation of lockdown with no exit strategy would substantially increase the case count and incur higher health and economic loss, even if the disease prevalence could be pushed down to pre-relaxation level by rounds of tightening of control measures [9]. Gradual release exit strategies tailored to local situations should be implemented to provide sufficient planning for public health authorities and governments to alleviate the burden of social and economic well-being from lockdown.

Declaration of Competing Interest

We declare no competing Interest.