Restrictions on Social Activities Delay Epidemic Peak of COVID-19

In a study, published in The Lancet, researchers examined how population mixing has affected outbreak progression of the coronavirus disease 2019 (COVID-19) in Wuhan, finding that if restrictions on activities were maintained until April, the epidemic peak would probably be delayed.¹

These projections suggest that premature and sudden lifting of interventions put in place could lead to an earlier secondary peak, which could be flattened by relaxing the interventions gradually. 

“Non-pharmaceutical interventions based on sustained physical distancing have a strong potential to reduce the magnitude of the epidemic peak of COVID-19 and lead to a small number of overall cases,” the authors wrote. “Lowering and flattening of the epidemic peak is particularly important, as this reduces the acute pressure on the health-care system.”

Researchers used synthetic location-specific contact patterns in Wuhan to examine changes in population mixing affected by the outbreak and adapted them in the presence of school closures, extended workplace closures, and a reduction in mixing in the general population. They then simulated the ongoing trajectory of an outbreak in Wuhan using an age-structured susceptible-exposed-infected-removed (SEIR) model for several physical distancing measures. 

Moreover, the researchers fitted the latest estimates of epidemic parameters from a transmission model to data on local and international exported cases from Wuhan in an age-structured epidemic framework and assessed the age distribution of cases. Simulations were also used to lift the control measures by allowing people to return to work in a phased-in way and looked at the effects of returning to work at different stages of the underlying outbreak (at the beginning of March or April). 

The projections indicated that physical distancing measures were most effective if the staggered return to work began at the beginning of April, reducing the median number of infections by more than 92% (IQR 66-97) and 24% (13-90) in mid-2020 and end-2020, respectively.

According to the researchers, benefits to sustaining these measures until April included delaying and reducing the height of the peak, median epidemic size at end-2020, and affording health-care systems more time to expand and respond. However, researchers also indicated that the modelled effects of physical distancing measures vary by the duration of infectiousness and the role that school children have in the epidemic. 

“Although the precise effects of interventions might vary by country and different estimates of key parameters, our model highlights the usefulness of physical distancing interventions and the need to carefully calibrate their lifting to avoid second and subsequent waves of a COVID-19 epidemic,” the authors wrote. “Policy makers are advised to reapportion their resources to focus on mitigating the effects of potentially soon-to-be overwhelmed health systems.” 

Researchers indicated that they did not incorporate climatic factors into their mathematical model, and future research should be directed towards understanding the possible seasonality of COVID-19 and the climatic factors that could affect its transmission dynamics. Additionally, the extent to which various strategies can detect cases of the virus earlier and isolate infectious individuals from the susceptible pool or protect against infection are not well understood, also necessitating further evaluation. 

“As more data emerge to inform these and all relevant parameters that influence transmission of this novel coronavirus, models can more accurately predict the success or failure of different strategies to control the epidemic and limit mortality,” Tim Colbourn, PhD, associate professor of global health epidemiology and evaluation at the UCL Institute for Global Health, wrote in an editorial commentary.² “Such models and projections should be made available in the public domain without delay to inspire public trust and allow wider potentially beneficial input. We need coordinated national and global efforts to rapidly model solutions to the grave predicament we now find ourselves in.”

Reference:

1. Prem K, Liu Y, Russell TW, et al. The effect of control strategies to reduce social mixing on outcomes of the COVID-19 epidemic in Wuhan, China: a modelling study. The Lancet. doi:10.1016/S2468-2667(20)30073-6.

2. Colbourn T. COVID-19: extending or relaxing distancing control measures. The Lancet. doi:10.1016/S2468-2667(20)30072-4.