Relaxing social distancing rules and lifting coronavirus closures in Wuhan, China — where the outbreak emerged — too soon could fuel a second wave of infections, according to a new study, published in the Lancet Public Health journal, suggesting that things should not go back to normal in Wuhan before April.

In December, 2019, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a novel coronavirus, emerged in Wuhan, China. Since then, the city of Wuhan has taken unprecedented measures in response to the outbreak, including extended school and workplace closures.

The researchers aimed to estimate the effects of physical distancing measures on the progression of the COVID-19 epidemic, hoping to provide some insights for the rest of the world.

To examine how changes in population mixing have affected outbreak progression in Wuhan, they used synthetic location-specific contact patterns in Wuhan and adapted these in the presence of school closures, extended workplace closures, and a reduction in mixing in the general community.

Using these matrices and the latest estimates of the epidemiological parameters of the Wuhan outbreak, they simulated the ongoing trajectory of an outbreak in Wuhan using an age-structured susceptible-exposed-infected-removed (SEIR) model for several physical distancing measures.

They fitted the latest estimates of epidemic parameters from a transmission model to data on local and internationally exported cases from Wuhan in an age-structured epidemic framework and investigated the age distribution of cases, also simulating lifting of 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).

Projections show that physical distancing measures were most effective if the staggered return to work was at the beginning of April; this reduced the median number of infections by more than 92% (IQR 66–97) and 24% (13–90) in mid-2020 and end-2020, respectively.

There are benefits to sustaining these measures until April in terms of 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, the modelled effects of physical distancing measures vary by the duration of infectiousness and the role school children have in the epidemic.

Restrictions on activities in Wuhan, if maintained until April, would probably help to delay the epidemic peak. Projections suggest that premature and sudden lifting of interventions could lead to an earlier secondary peak, which could be flattened by relaxing the interventions gradually.

However, there are limitations to analysis, including large uncertainties around estimates of R 0 and the duration of infectiousness.

Bill & Melinda Gates Foundation, National Institute for Health Research, Wellcome Trust, and Health Data Research UK.

“The city now needs to be really careful to avoid prematurely lifting physical distancing measures, because that could lead to an earlier secondary peak in cases,” Kiesha Prem, a specialist at the London School of Hygiene & Tropical Medicine (LSHTM), who co-led the research, told Reuters.

“If they relax the restrictions gradually, this is likely to both delay and flatten the peak.”

The researchers conducted the study by using mathematical modeling to simulate either extending or relaxing school and workplace closures in Wuhan, which is home to 11 million people.