Social distancing may be enforced again in 2022 as coronavirus could rebound once measures are lifted: Study
Experts feel such measures may have to stay in place over long periods, perhaps with occasional periods of loosening, as immunity slowly accumulates in the population to a point where it would preclude future outbreaks
The coronavirus pandemic is straining healthcare resources globally prompting social distancing measures — avoiding large gatherings and close contact with others — to slow down the spread of the virus. However, the amount of social distancing needed to curb the outbreak in the context of seasonally varying transmission remains unclear.
Now, a group of US researchers says that one-time social distancing will not be sufficient to prevent critical care capacities from being overwhelmed. The reason: once such restrictions are lifted, the virus would, in all probability, come roaring back. Accordingly, says the research team, on its own, social distancing may need to be maintained intermittently into 2022 to avoid overwhelming critical care capacity.
The team — which includes experts from the Harvard TH Chan School of Public Health, Boston, US — explains that increased capacity across hospitals and additional interventions such as contact tracing, therapeutics, and vaccines are urgently needed to ease this burden.
“A single period of social distancing will not be sufficient to prevent critical care capacities from being overwhelmed by the COVID-19 epidemic, because under any scenario considered, it leaves enough of the population susceptible that a rebound in transmission after the end of the period will lead to an epidemic that exceeds this capacity. This resurgence could be especially intense if it coincides with a wintertime rise in reproductive rate,” say the researchers in their findings, a pre-print of which has been published.
What is social distancing?
With no treatments or vaccines available, interventions have focused on contact tracing, quarantine, and social distancing.
Intensive testing, tracing, and isolation of cases has enabled control of transmission in some places, such as Singapore and Hong Kong. At the opposite extreme, many countries lack the testing and public health resources to mount “similar responses to the COVID-19 epidemic, which could result in unhindered spread and catastrophic outbreaks.”
Between these responses, many countries are adopting what is being referred to as “social distancing” or “physical distancing” by closing schools and workplaces and limiting the sizes of gatherings.
The goal of these strategies is to slow the spread of infection and reduce the intensity of the pandemic — flatten the curve — thus reducing the risk of overwhelming health systems and buying time to develop treatments and vaccines.
“However, there is concern that such measures may have to stay in place over long periods, perhaps with occasional periods of loosening, as immunity slowly accumulates in the population to a point where it would preclude future outbreaks,” say experts.
What did the researchers find?
The researchers explain that the transmission of many respiratory pathogens, including the human coronaviruses that cause mild common cold-like syndromes, is seasonal in temperate regions and peaking in the winter months. While not much is known as to how COVID-19 will eventually behave, the experts say if COVID-19 transmission is similarly subject to “seasonal forcing,” summer outbreaks would naturally have lower peaks than winter outbreaks.
The researchers argue that seasonal variation in transmission will facilitate outbreak control during the summer months, but could lead to an intense resurgence in the autumn.
“Due to seasonal variation in transmission strength, it may be more difficult to flatten epidemic curves in the winter than in the summer. Moreover, a winter peak for COVID-19 will coincide with peak influenza, further straining healthcare systems,” says the study.
The experts further say a key metric for the success of strategies meant at reducing the intensity of the transmission is whether critical care capacities are exceeded. And to keep critical care capacities from being overwhelmed, prolonged or intermittent social distancing may be necessary.
To determine this in the context of COVID-19, the research team used a mathematical model to simulate the transmission of COVID-19 in the US.
The model attempted to answer questions such as how long do social distancing measures need to stay in place and how is this affected by seasonality. “We assessed the transmission of COVID-19 through 2021 using a mathematical model with seasonal transmission forcing,” they explain. The experts found that under different scenarios, there was a resurgence of infection when the simulated social distancing measures were lifted.
Based on these projections, the team says in the absence of the development of new therapies, vaccines, or preventative measures such as aggressive contact tracing and quarantining, intermittent distancing measures may be the only way to avoid overwhelming critical care capacity. And these measures may well go into 2022.
“Intermittent social distancing can maintain the prevalence of critical COVID-19 illness within current capacities, but (without other interventions) this strategy could prolong the overall duration of the epidemic into 2022. Increasing critical care capacities would substantially reduce the overall duration of the epidemic while ensuring adequate care for the critically ill,” says the team.
Explaining the analysis, study author Stephen Kissler says that the findings are in agreement with a recent report that said strong, one-time social distancing may suppress critical cases to within capacity, but the infection will resurge and overwhelm capacity once measures are lifted.
“We show that if social distancing is relaxed when transmissibility is heightened in the fall, an intense winter outbreak may occur in the still mostly-susceptible population. This peak may be higher than the ‘no intervention’ case and will overlap with flu season,” he tweeted.
Kissler says that intermittent social distancing can prevent critical care capacity from being exceeded but such measures may be required for 12-18 months. “Depending on the reproductive rate and the amount of seasonality, social distancing must be ‘on’ for as little as 25% but up to 70% of the time,” he says.
The team says the timing and duration of the interventions will likely need to be tailored geographically due to variation in epidemic timing, seasonal forcing, and critical care capacities.
The second report by researchers from Imperial College London, UK, also says that the effectiveness of any one intervention in isolation is likely to be limited, requiring multiple interventions to be combined to have a substantial impact on transmission.
It says the major challenge of an intensive intervention package — such as social distancing, home isolation/quarantine, school, and university closures — will need to be maintained until a vaccine becomes available, potentially 18 months or more, “given that we predict that transmission will quickly rebound if interventions are relaxed.”