Significant new model of COVID-19 spread influences UK & US responses

A new report, from the world’s leading epidemic modeling group at Imperial College London, is suggesting intensive active suppression, including isolation of all cases and extreme social distancing measures, may be the most effective immediate intervention to reduce mortality and healthcare demand as the COVID-19 pandemic continues to spread. The new data, reportedly influencing both US and UK government policy, recommends suppression measures may have to be intermittently turned on and off over the next 18 months until a vaccine is developed and mass immunity occurs.

“The world is facing the most serious public health crisis in generations,” explains Neil Ferguson, head of the MRC Centre for Global Infectious Disease Analysis at Imperial College London. “Here we provide concrete estimates of the scale of the threat countries now face.”

The report presents the results of a model examining the potential effect of several public health measures on viral transmission rates and mortality. Two overall strategies are discussed in the paper: mitigation and suppression.

Mitigation involves a community working to slow the spread of the virus through measures such as isolating confirmed cases, and social distancing of the elderly and those in high-risk groups. The goal of mitigation is not to actively suppress or stop infections but rather protect those most at risk while still allowing moderate spread of the virus until population immunity builds up leading to a decline in case numbers.

Suppression, on the other hand, aims to halt human-to-human transmission through more extreme social distancing and quarantine measures. This can include shutting down non-essential services, closing schools, and keeping people separated by isolating the entire population in their homes.

The challenge governments around the world currently face is finding the most effective balance between these two general strategies. The big finding coming out of the new report is that the most optimal mitigation strategy may still result in an overwhelming load on healthcare systems and large volumes of fatalities.

“In the most effective mitigation strategy examined, which leads to a single, relatively short epidemic (case isolation, household quarantine and social distancing of the elderly), the surge limits for both general ward and ICU beds would be exceeded by at least 8-fold under the more optimistic scenario for critical care requirements that we examined," the report concludes. "In addition, even if all patients were able to be treated, we predict there would still be in the order of 250,000 deaths in GB, and 1.1-1.2 million in the US.”

So, more active suppression strategies may be necessary, however, the obvious question for these kinds of more stringent measures is, how long can they be maintained?

The modeling in the report affirms that major suppression strategies can work to reduce viral transmission. These measures include closing schools and universities, and instituting mass social distancing by keeping the majority of the population at home in isolation. The problem is that the modeling suggests the epidemic will spike again as soon as these measures are relaxed. And with a vaccine potentially 18 months away, the social, economic and psychological costs of long-term mass population quarantine is obviously immense.

The ultimate recommendation from the report is that major suppression measures must be instituted initially, in order to slow the spread of the virus. While it is unfeasible to continue these strident measures indefinitely, the report suggests active local monitoring of confirmed cases will inform when to loosen those measures and when to tighten them back up, in a strategy analogous to turning a tap on and off.

“To avoid a rebound in transmission, these policies will need to be maintained until large stocks of vaccine are available to immunize the population – which could be 18 months or more,” the report suggests. “Adaptive hospital surveillance-based triggers for switching on and off population-wide social distancing and school closure offer greater robustness to uncertainty than fixed duration interventions and can be adapted for regional use (e.g. at the state level in the US). Given local epidemics are not perfectly synchronized, local policies are also more efficient and can achieve comparable levels of suppression to national policies while being in force for a slightly smaller proportion of the time.”

While the report certainly concludes, with no doubt, that “epidemic suppression is the only viable strategy at the current time,” the researchers are clear in stating these recommendations can swiftly change as we learn more about how the virus functions, and how we can effectively fight back.

Countries such as China and South Korea are also noted as important examples of suppression measures working effectively in the short term, however, researchers are watching those nations closely to monitor the broad effects of loosening those extreme measures. China, in particular, has demonstrated major success with extreme suppression measures but it is yet to be seen whether the disease will spike again once those measures are relaxed.

CNN reports this comprehensive modeling study has been passed on to both UK and US governments. The White House Coronavirus Task Force is reportedly currently discussing the contents of the report. The UK government, on the other hand, has swiftly shifted its overall approach based on some of the modeling in the report.

The UK’s government’s initial response to the virus was one of lighter mitigation measures. The plan was to allow certain spreads of infection in order to speed up the process of herd immunity. However, in response to this new report, the UK government is now rapidly rolling out social distancing measures, calling for those in the highest risk categories to self-isolate.

“We have to accept that COVID-19 is a severe infection and it is currently able to spread in countries such as the US and the UK,” says Steven Riley, a professor of infectious disease dynamics working on this latest report. “In this report, we show that the most stringent traditional interventions are required in the short term to halt its spread. Once they are in place, it becomes a common priority for us all to find the best possible ways to improve on those interventions.”

The report ultimately makes clear this global pandemic will need dynamic long-term management. The current model hypothesizes active suppression measures may be necessary for two-thirds of the next 12 to 18 months until a vaccine appears.

In a March 9 address, the Director General of the World Health Organization stressed how each country will need to institute its own tailored response. And that response will not simply be based on a binary choice between trying to contain the virus and trying to mitigate its impact. Instead, the most likely outcome is a dynamic interplay responding to local ups and downs in infection rates.

“Different countries are in different scenarios, requiring a tailored response,” said the Director General. “It’s not about containment or mitigation – which is a false dichotomy. It’s about both. All countries must take a comprehensive blended strategy for controlling their epidemics and pushing this deadly virus back.”

The new modeling report is available here.

Source: Imperial College London