COVID-19: to contain or delay and mitigate, which is the best strategy?

Updated on March 27th 2020, written by Dr David Owens.

In a previous article, I described the principles used in the management of new epidemics of infectious disease. There are currently differences in international public health controls. Countries and organizations were previously reacting in a way which lacked clarity and coordination. There is now more consensus although there are still some fundamental differences in strategy.

For simplicity I will briefly summarize my initial analogy of the epidemic as a series of fires which have seeded from the initial blaze in Wuhan. The main fire in Wuhan and Hubei province has been brought under control, as have smaller clusters in Hong Kong in Singapore and on the Diamond Princess cruise ship. Currently, more than 50% of the fires are burning in Europe although there are also outbreaks all over the world.  We have learned valuable lessons about methods that help to control the fires and we also have a much better idea about how much damage the fire does in certain circumstances. We are now faced with a decision as to whether to tell everybody to stay in their fire proof bunkers or whether we slowly try to get some people back to work. This is a question of relative risks. The damage caused by the fire or the economic and social damage of inactivity and fear.

This is the playbook typically described by the WHO1 for the management of epidemics of infectious disease:

Containment: Effective and rapid containment of emerging diseases is just as vital as early detection in order to avoid a large scale epidemic. Rapid containment should start as soon as the first case is detected regardless of the cause, which is most likely to be unknown. It requires skilled professionals to safely implement the necessary countermeasures. Pre-training of these professionals is essential to guarantee the safety and efficiency of the operations.

Control and mitigation: Once the infectious disease threat reaches an epidemic or pandemic level, the goal of the response is to mitigate its impact and reduce its incidence, morbidity and mortality as well as disruptions to economic, political, and social systems.

Elimination or eradication: Control of a disease may lead to its elimination, which means that it is sufficiently controlled to prevent an epidemic from occurring in a defined geographical area. Elimination means that the disease is no longer considered as a major public health issue. However, intervention measures (surveillance and control) should continue to prevent its re-emergence.

I described the balance which countries must navigate in assessing the risk to the population in terms of the human and economic impact of the disease versus the economic, social and political impact of the containment measures.

‘Returning to normal will be determined by an increasing understanding of the epidemic and a balance between the threat of the disease and the cost of the public health controls in both human and economic terms. The move to local containment and mitigation and control will involve a shift in messaging and will require education and communication.’

Methods of containment invariably involve political decisions. Restriction of movement and quarantine are decisions which balance the rights of the individual against the rights of the majority. In order to explain this process, I will attempt to outline the relative arguments that inform the differing perspectives. Again, I wish to emphasize that I am a doctor, with a community health bias. It is neither within my remit nor am I trying to make any political points. A rational understanding of this process involves an acknowledgement of both implicit and explicit bias and an awareness of the inevitable underlying political narrative in the control of infectious disease.

The argument for containment:

Containment of the epidemic has the following aims:

  1. The lower the epidemic size (number of people infected) the lower the number of people who will become ill and the lower the total mortality.

  2. Slowing the evolution of the epidemic buys time in order to:

    1. develop tests to help us better understand the nature of the infection and the optimal control methods
    2. develop treatments to optimally manage the illness
    3. prepare health systems and in the case of COVID-19 ideally nudge the peak of the COVID-19 epidemic past that of influenza, in order to prevent overload of intensive care and high dependency medical units
    4. develop a vaccine which is ultimately one of the most effective methods of controlling epidemics of infectious disease.

  3. The lower the epidemic size the higher the likelihood of it dying out naturally. This may be influenced by environmental factors. For example, coronavirus infections often die out in Spring with an increase in warmer and more humid weather.

  4. The lower the absolute volume of circulating virus the lower the risk of viral mutation.

Countries develop preparedness plans for containment of epidemic illness and, as is inevitable, there is a difference in the capacity of preparedness. It is important to understand that the early containment in China went beyond the lockdown of cities and restriction of movement. Teams of epidemiologists put in place a systematic response of contact tracing and quarantine. 1,800 epidemiology teams of five people per team in Wuhan alone. I have received a number of criticisms regarding my use of China data. I explicitly acknowledge that any data analysis is dependent on the integrity and validity of the data. I would encourage anyone who has an interest in this area to read the WHO report on the China response and draw their own conclusions3.

We have seen the relative controversy of the delayed containment strategies in Italy. Faced with a health system under severe strain due to the COVID-19 epidemic hitting during an ongoing severe influenza epidemic the government opted for aggressive short term social distancing strategies in order to delay and smooth out the peak of cases. A further example of the case for containment is Korea where there have currently been 316,664 tests undertaken, confirming 9,332 cases of COVID-19 and currently tracking at a mortality of 1.5%.

Hong Kong and Singapore are two geographic entities which share many similarities, amongst which are world class systems and expertise in the control of infectious disease. Both systems have strong public health legislation, highly developed preparedness plans and (notwithstanding the recent unrest in Hong Kong), a strong tradition of civic responsibility and acceptance of some degree of limitation of individual autonomy in order to facilitate a benefit to the majority. Possibly the most obvious example being the widespread acceptance of identity cards which have historically played an important role in control of infectious disease in Hong Kong (by facilitating contact tracing and quarantine). It is generally accepted that public health controls helped to prevent a more severe epidemic spread of SARS in 2003.

The Hong Kong government currently has a strategy to minimise imported cases as much as possible. Catch, detain and quarantine and attempt to control local spread such that the disease has no local impact or as little impact as is possible.

The DG of the WHO emphasized the importance of preparedness and not giving up on containment strategies in his speech to announce that COVID-19 is a pandemic. He has emphasized the importance of testing for case identification in addition to ongoing quarantine.

The argument for delay, control and mitigation:

‘Once the infectious disease threat reaches an epidemic or pandemic level, the goal of the response is to mitigate its impact and reduce its incidence, morbidity and mortality as well as disruptions to economic, political, and social systems.’ - World Health Organization

During the 2009 H1N1 Swine Flu pandemic a significant amount of time went into containment. The catch, isolate and treat response. The subsequent UK Influenza Pandemic Preparedness Strategy 2011 took lessons from this process and emphasised the need to maintain the continuity of essential services and continue everyday activities as far as possible4. A recent editorial in the Lancet by Wilder-Smith from the London school of tropical medicine reached a similar conclusion regarding COVID-19 suggesting the need to move to mitigation5. In another paper in the Lancet6, Anderson argues that the UK has already moved in to the delay and mitigate phase of management as have Italy, South Korea, Japan, and Iran. The graph below, from this article demonstrates the intention of social distancing to flatten the size of the epidemic curve which can take the strain off health systems.

epidemic simulation with preventative means

Figure 1 - A baseline simulation with case isolation only (red); a simulation with social distancing in place throughout the epidemic, flattening the curve (green), and a simulation with more effective social distancing in place for a limited period only, typically followed by a resurgent epidemic when social distancing is halted (blue). 

Bhatia and colleagues at Imperial college have produced a frequently cited epidemiological study that estimates that up to two thirds of exported cases from the initial China clusters may have been unrecognised7.

The argument here would essentially say, the disease is now spreading. Total containment will not be possible. Fortunately, we have more understanding about this illness. It seems less severe than first thought. It will have a relatively low mortality except in those who are older and with other illness. We also know that above a certain threshold the immunity of the population stops an epidemic from being able to take hold. In the real world this number will be impacted by unpredictable factors in the epidemic including the public health measures, climate and the potential natural attenuation (weakening) of the virus with time. As a rule of thumb an infectious illness with R0 of 2 will begin to die as 50% of the population acquire immunity. For R0 of 3 the number rises to around 66%. This is the concept of herd immunity which forms a part of the UK strategy. This is not however the whole strategy. The UK is advocating targeted social distancing measures to flatten the curve, isolate vulnerable and elderly patients whilst maintaining some degree of social mixing such that the less vulnerable members of the community develop immunity. At the same time shifting resources towards hospital care rather than widespread testing and managed quarantine.

Against this we must consider that poverty is the single most important determinant of global health9 and economic growth is the most powerful determinant for reducing poverty10. Taking the utilitarian view we could immunise every child in the world for a tiny fraction of the economic impact of this disease and if we do not ameliorate this economic impact we will add to this burden.

So what will happen?

The UK, Europe and the US effectively moved directly into delay and mitigation. There were different local decisions in terms of controlling crowd sizes, limiting travel, school closures and local quarantine but the explicit strategy was to use public health controls to supress the COVID-19 peak in order to control the surge on health systems. It seems likely that the majority of traditional Western democracies and most other countries will use measured public health containment and mitigation strategies to flatten and smooth the epidemic peak but will essentially let the epidemic burn through whilst trying to minimise overload of health systems and maintaining economic activity. The relatively relaxed initial policies of the UK were changed relatively quickly in response to the severity of the epidemic in Italy in addition to the publication of an epidemiological study from Imperial College London which predicted overwhelming cases in the hospital system without greater levels of public health regulation11. A more recent publication from Oxford projects a higher degree of existing herd immunity. It is too early to be certain which model will be closer to the way the epidemic plays out on the ground12.

Essentially, we have an academic debate in public health circles which is playing out on the world stage. The WHO have clearly adopted a policy based upon testing, isolation and quarantine to contain the disease. This has been successful in China, Hong Kong, Singapore and Korea and provides a model for reducing the total epidemic size. This buys time to get more information on the best containment and mitigation strategies, develop testing, research treatments and work on a vaccine whilst also hoping that natural environmental factors help in reducing the epidemic. The counter argument is that once the disease has ‘escaped’ the containment phase the populations in the locked down communities will not be able to stay protected forever without the isolation having a significant impact on social and economic life. Unless the disease dies or a vaccine is developed the non-immune populations will eventually need to acquire immunity. The results of these different strategies in addition to the differing methods of social distancing and isolation will provide useful information in managing not only this epidemic, but future epidemics of new disease.

Here is a very simple bottom up example. Any patient diagnosed with COVID-19 in Hong Kong is admitted to hospital regardless of their symptoms. Typically for more than two weeks. All their close contacts are quarantined in government centres. In the UK they are sent home, they and their family members are told to self-isolate, wear a mask and are only admitted to hospital if they are in the small number that develop complications. The arguments are that the UK strategy may not prevent community spread as effectively as Hong Kong. The counterargument is the majority of patients have mild symptoms. If >80% of Hong Kong cases could be managed at home that is >1000 hospital bed days. How many people are having treatment for cancer, heart disease or other conditions delayed and how will that measure against the disease burden of COVID-19? The same principles play out across the civil service, court systems and ultimately the functioning of the economy. The Hong Kong counter argument is that the hospitals are able to function exactly because they have managed to control the local epidemic size.

Is this the correct approach?

There are many unknowns but my personal analysis is that what will almost inevitably happen is also the best option in the long term. The obvious infectivity of this disease from epidemic clusters must in my opinion represent a significant degree of, as yet unrecognised mild illness, which will by definition make the final mortality lower than is currently predicted from the current cohorts.

All public health interventions involve an analysis of cost and benefit and one of the key factors in the control of infectious disease is to strive to minimize population mortality whilst also minimizing adverse impact on social, political and economic systems. Ultimately the single greatest determinant in population health is poverty and any population based intervention which ignores the economic impact runs the risk of doing more harm than good.

COVID-19 has killed 22,538 people in comparison to Influenza which kills 650,000 people every year. COVID-19 is not an influenza infection and we do not yet have a vaccination. It seems to be more severe on a case by case basis but until we have a better understanding of the number of mild cases we do not know that for certain. The final mortality will be determined by the epidemic and will be influenced by environmental factors in addition to social distancing and other public health controls. Again, I wish to emphasize that I am not in any way belittling the importance of this disease as a global public health challenge. The nature of this illness is that it will place a significant burden on health systems. The main goal of the current social distancing measures is to flatten the curve and take the pressure off health systems. If we do not want the economic and social fallout of the public health measures to do more harm than the disease itself we will eventually need to focus on restoring economic function and we will need to move towards mitigation rather than a focus on containment. Managing this epidemic will be a balance between mitigating the impact of the disease, both on individuals and the health system, whilst minimising the impact of the public health controls on the social and economic life of Hong Kong.

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All our public health information regarding COVID-19 is also available in Chinese here.

References

  1. World Health Organization. (2018). Managing epidemics: Key facts about major deadly diseases. Retrieved February 26, 2020, from https://www.who.int/emergencies/diseases/managing-epidemics-interactive.pdf
  2. Institute of Medicine (US) Forum on Microbial Threats. (1970, January 1). Strategies for Disease Containment. Retrieved February 26, 2020, from https://www.ncbi.nlm.nih.gov/books/NBK54163/
  3. Report of the WHO-China Joint Mission on Coronavirus Disease 2019 (COVID-19) . (2020, February 24). Retrieved March 11, 2020, from https://www.who.int/docs/default-source/coronaviruse/who-china-joint-mission-on-covid-19-final-report.pdf
  4. Watkins, J. (2020, February 28). Preventing a covid-19 pandemic. Retrieved from https://www.bmj.com/content/368/bmj.m810
  5. Wilder-Smith, P. A., Chiew, C. J., & Lee, V. J. (2020, March 5). https://www.thelancet.com/journals/laninf/article/PIIS1473-3099(20)30129-8/fulltext. Retrieved from Can we contain the COVID-19 outbreak with the same measures as for SARS?
  6. Anderson, R. M., Heesterbeek, H., Klinkenberg, D., & Hollingsworth, T. D. (2020, March 9). How will country-based mitigation measures influence the course of the COVID-19 epidemic? Retrieved from https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(20)30567-5/fulltext
  7. Imperial College London. (n.d.). Retrieved from https://www.imperial.ac.uk/mrc-global-infectious-disease-analysis/news--wuhan-coronavirus/
  8. 2019 Novel Coronavirus (2019-nCoV) Situation Summary. (2020, March 9). Retrieved from https://www.cdc.gov/coronavirus/2019-nCoV/summary.html
  9. Poverty and social determinants. (2020, March 5). Retrieved March 5, 2020, from http://www.euro.who.int/en/health-topics/environment-and-health/urban-health/activities/poverty-and-social-determinants
  10. Department for International Development. (n.d.). BUILDING JOBS AND PROSPERITY IN DEVELOPING COUNTRIES. Retrieved March 5, 2020, from https://www.oecd.org/derec/unitedkingdom/40700982.pdf
  11. Imperial College COVID-19 Response Team. (2020, March 16). Impact of non-pharmaceutical interventions (NPIs) to reduce COVID19 mortality and healthcare demand. Retrieved from https://www.imperial.ac.uk/media/imperial-college/medicine/sph/ide/gida-fellowships/Imperial-College-COVID19-NPI-modelling-16-03-2020.pdf
  12. Fundamental principles of epidemic spread highlight the immediate need for large-scale serological surveys to assess the stage of the SARS-CoV-2 epidemic. (n.d.). Retrieved from https://www.dropbox.com/s/oxmu2rwsnhi9j9c/Draft-COVID-19-Model (13).pdf?dl=0

 

Topics: Hong Kong Health, COVID-19

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