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Researchers in Scotland who have evaluated a ‘stratify and protect’ policy to combat coronavirus disease 2019 (COVID-19) in the UK say it is time to seriously consider the approach as an alternative to social distancing.
Glasgow / Scotland – April 04, 2020: Glasgow City Center Buchanan Street empty during Covid 19 Coronavirus Block. Image credit: Mo and Paul / Shutterstock
The strategy would involve protecting elderly and high-risk people from infection, while allowing exposure and immunity to grow among low-risk people until the majority of the population is protected.
“It is time to seriously consider a layering and protection policy that could end the COVID-19 epidemic in a matter of months while restoring economic activity, avoiding the overload of critical care services and limiting mortality,” says Paul McKeigue and Helen Colhoun from the University of Edinburgh.
A preprinted version of the paper is available at MedRxiv, while the article undergoes peer review.
Probability tree for a stratify and protect policy
The different approaches
The researchers say that the epidemic will only pass if the population’s immunity reaches a level where the number of reproduction (number of cases of secondary infection derived from an original case) decreased to less than 1, either as a result of the natural immunity or immunization.
Although the blockade has slowed the spread of COVID-19, many disease model experts agree that to keep the pressure on critical care services at a manageable level, alternating periods of more and less social distancing measures will be needed. strict until an available vaccine is applied.
However, an effective vaccine is not expected to be available for at least a year.
Concerns about the economic and social impact of alternative blocking measures taken in the meantime have led researchers to consider other approaches to managing the epidemic.
An alternative that has been suggested is to impose more intense measures on high-risk people while allowing low-risk people to be exposed to the infection until the majority of the population has developed immunity. The idea would be to protect against any second wave of SARS-CoV-2, once the epidemic has passed while easing the strain on the NHS.
Investigate the theoretical dependencies of politics.
Now McKeigue and Colhoun have evaluated the effectiveness of the policy in minimizing the death rate if the rules of social distancing were relaxed. The approach would use a medical record data-based classifier to assign risk levels to individuals to determine who should not be protected.
“We do not advocate a particular course of action,” writes the team … “but we investigate the theoretical dependencies of the stratify and protect approach, its possible impact on mortality and workload for the health service, and discuss how to resolve some of the key uncertainties on which the effectiveness of such an approach depends. “
The analysis found that the proportion of the population that would be protected under the policy would be no more than 15%. However, even if a classifier based on medical record data performed only slightly better than one based only on age and gender, it should still be possible to refer at least 80% of those who would die unprotected to the protection group.
The importance of the mortality rate in the entire population
The average risk of infection among protected individuals and the total number of deaths while the shield is implemented would completely depend on the mortality rate in the entire population.
“Although the proportion of deaths that would be avoided by effective shielding does not vary much with the infection death rate, the absolute number of deaths in the unprotected varies from less than 10,000 if the infection death rate is 0.1% to more than 50,000 if the infection death rate is as high as 0.4%, ”the team writes.
If the ratio were at the high end of the values now considered viable (0.4%), even a well-performing classifier could not guarantee that deaths would remain below 30,000 or reduce the risk of death among people without armor . than 1 in 2000, although this would still be manageable through the expansion of critical care services
However, the researchers note that mortality risk predictions for unshielded individuals are averaged across the group and that a risk classifier “could, of course, generate not only a dichotomous classification, but a continuous risk score that would be the basis for individual choice. “
“Any protection strategy involves questions of ethics and equity in the sense that members of the unshielded group are asked to accept a low risk so that not only they, but those protected against infection, can get out of isolation sooner” McKeigue and Colhoun write.
The team says researchers currently conducting studies that should help answer important questions about applying the layer-and-protect approach. Areas of uncertainty include the prevalence of immunity, the degree to which infection results in immunity, the death rate, and the performance of a classifier based on medical history.
“This policy option should not be ruled out”
The researchers say the time has come to seriously consider a layering and protecting policy that could hasten the end of the COVID-19 epidemic.
“A layering and protection policy that uses a medical record-based classifier has the potential to save lives, restore economic activity, and end the epidemic long before a vaccine is expected to be available,” they write. “This political option should not be ruled out, but seriously evaluated as an alternative to adaptive social distancing.”
Important news
medRxiv publishes preliminary scientific reports that are not peer reviewed and are therefore not considered conclusive, guide clinical practice / health-related behavior, or are treated as established information.
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