A new study published in the preprint journal medRxiv in April 2020 explores the possibilities of launching smaller waves of voluntary social exposure in a controlled way, to avoid the occurrence of a single large and probably unmanageable second wave of infection.
Suppression vs. mitigation
Lockdowns and mandatory social distancing have become part of life in many countries, with the COVID-19 pandemic still in full flow. These “suppression” measures have bought some time for the healthcare systems to build capacity and brought down death rates to some extent. Yet their economic and social impact may be insufferable to the eyes of some experts.
A second approach is called “mitigation,” and refers to the quarantine of infected people, voluntary isolation at home, and social distancing of populations at risk.
The problem with mitigation is that it brings down the peak demand for intensive or critical care of patients to a level that is inadequate to relieve the staggering burden on healthcare systems. The issue was grimly illustrated in the catastrophic death rates in Italy, Spain, France, and the US.
All these countries shifted to suppression mode later to effectively control the spread of the virus. The biggest problem with this approach is that it prevents herd immunity from developing while arresting a colossal segment of economic activity and paralyzing social functioning.
Of course, some smaller nations have successfully used the mitigation strategy to deal with the pandemic while controlling the case fatality, though, unlike China, the number of cases has not come down to negligible levels so far.
The importance of herd immunity
The researchers say that without a vaccine, the COVID-19 pandemic will be difficult to contain since it has a high rate of spread as well as a large percentage of asymptomatic and presymptomatic but infectious cases. The only way out is to achieve herd immunity, where 58% to 70% of the low-risk population is infected while shielding the high-risk segment, which has a likelihood of poor or fatal outcomes. This will ensure that healthcare resources are used optimally throughout this phase.
What is the controlled avalanche approach?
The current study argues for another method of control, which relies on voluntary viral exposure in supervised conditions, for healthy people aged 20-49 years, to produce herd immunity. These are the lowest-risk category. If successfully infected, they will be given immunity certificates, which allow them to leave quarantine.
The researchers use a compartmental model to analyze the fallout of the “controlled avalanche (CA)” plan in the Israeli population. The controlled avalanche is a practice seen at ski resorts, “which intentionally triggers small avalanches in order to prevent a singular catastrophic one.”
How does the CA approach work?
The underlying assumptions of this model are:
- Infection with SARS-CoV-2 immunizes those who recover for a long time, similar to the SARS virus.
- Infected cases remain infectious for a limited time (up to 14 days from the first clinical symptoms), and virus shedding can be picked up quickly.
- Case fatality among the 20-49 year population is very low, at 0.03% to 0.16%.
Given these assumptions, the researchers suggest the following strategy:
Low-risk individuals are allowed to encounter infection under controlled conditions if they so wish. This may be through relaxing social distancing and release from quarantine for the participants in order to contract the virus. They must, of course, be willing to quarantine subsequently and be monitored for infection.
If they are infected and recover, immunity certificates will be issued, and they can rejoin social, and workplace functioning without limitation, as well as assist in high-risk situations, including healthcare.
What are the possible outcomes?
They look at four potential situations. In the first two, the low-risk segment of the population is managed by the CA approach, while the rest of the people are still under restricted social interaction norms. Subsequently, either mitigation measures are extended to the whole population, or the virus is allowed to spread in an uncontrolled fashion.
The other two scenarios depict either a situation of mitigation or uncontrolled spread without CA. The probable results of this strategy in economic and public health terms are also explored.
How does CA help to control COVID-19?
The results show that the CA strategy brings down the death rate by over 40%. The peak number of intensive care unit admissions can be reduced by more than 60%, while more than half of the low-risk population can be incrementally released from quarantine within 2 months to return to work.
This model is important in that it proposes a practice for achieving herd immunity with reasonable speed, and faster than the practices being followed at present, while minimizing economic fallout and restricting the death rates.
The take-home message
Rather than opening public and workspaces to all low-risk groups, which would risk the spread of the virus in an uncontrolled manner, this model encourages governments to move to a CA program that combines low-risk exposure with mitigation of the general population.
Public education and understanding are paramount in this scenario. The government can redirect suppression resources into ensuring compliance with screening, exposure, and monitoring mechanisms while confirming recovery and issuing immunity certificates.
Moral compulsions also favor the CA model, in that there is a significant element of informed choice to expose oneself to a low risk of death in order to regain for oneself and for society as a whole greater freedom from a higher mortality rate, successful public health outcomes, and mitigation of the economic crisis.
The study concludes, “It is time for policymakers to include herd immunity as the main goal in the array of policy options. This will require a multi-sector, professional, and representative task force to manage policy options such as CA and the Covid-19 crisis in general.”
Important Notice
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
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