When is it time to ease controls? Epidemiological scenarios to consider

Is it necessary to sacrifice public health for the economy – or the economy for public health? It's a difficult tightrope COVID-19 is forcing the world to walk and finding the right footing isn't easy.

While governments and health officials wrestle with how long to maintain social distancing and consider what types of economic stimuli are needed, we modelled four scenarios across two sample countries, which show how lifting control measures too early could trigger a risky recurrence.

What impact will changing these restrictions have on deaths? What is clear from our projections is that these outcomes are asymmetrical – tightening the interventions saves some lives, while easing them too quickly could cost many more. The sensitivities are explored for Italy and Austria, which are at different stages of the crisis, and show how only a 10% relaxation of social distancing measures taken at the same time, may lead to significantly different outcomes.

Our conclusion across the two countries is the same. It's vitally important for governments to carefully consider timing of relaxation and hold lockdowns in place until new infections are below a critically low level. If not, the consequences could reverse all progress made during interventions and ultimately lead to many more deaths.

We will also address that reoccurring spreads of COVID-19 can be expected and that governments need to manage further spreads tightly to prevent countries from further lockdowns.

The epidemiology behind social distancing measures

There’s been a great deal of discussion about the types of measures used to prevent further spread of COVID-19, their effectiveness and the extent to which they are used. It helps to begin by understanding the objectives of these interventions from an epidemiological perspective1.

We know viral infections can grow exponentially. The average number of infections that result from each new infection in a fully 'susceptible' population is referred to as the basic reproduction number R0. Interventions (control measures) aim to force the effective reproduction number Rt below 1 over time to decrease the overall infection rate.

To show how interventions might affect the number of cases, we designed a simple epidemiological study with base assumptions on R0, the case fatality rate (CFR) by age and other key parameters pulled from various public reports2,3. The severity of the interventions can be assigned a factor, with 0 representing no interventions and 1 representing the most extreme interventions, resulting in an Rt of zero. The study is meant to spark questions and inform debate. It is not in any way a business model or insurance industry projection.

We simulate four different scenarios from April 24 to June 30:

  • Baseline scenario: government orders do not change over the projection period
  • Strengthen scenario: interventions strengthen by 10% after April 24
  • Weaken scenario: interventions relax by 10% after April 24
  • Variable scenario: interventions gradually relax, and strengthen over time, depending on the number of new infections

The modelling applied here is not intended to predict ultimate absolute mortality outcomes but to test sensitivities of the potential relative impacts from a relaxation if applied too early.

We have selected Italy, as the first affected European country, and Austria, the first European country to announce a relaxation of restrictions. All conclusions are the modelled impact of the interventions with an assumed level of severity based on the work by Neil Fergusson's group at Imperial College London and updated epidemiological reports from China and Europe4,5.

Our assumptions are based on reported mortality values, but these are fluid, with definitions and specifics frequently changing. In recent weeks, discussions have centred around the reporting of deaths in care and nursing homes, as well as revised figures from Wuhan, Spain, France and Italy6. There is also a debate on the rates of death that asymptotic carriers of COVID-19 may have.

Italy

Baseline scenario: Hospitalisation rates indicate higher mortality

Italy was the first European country to experience clusters of outbreaks of COVID-19. Lockdowns were ordered in the northern region of Lombardy beginning 21 February and slowly expanded into other areas, followed by a national lockdown order issued on 9 March. With promising daily numbers emerging in the second week of April, Italy is believed to be past the peak infection rate.

Figure 1 shows the baseline scenario and predicted spread in Italy through the end of May. This shows that the number of daily deaths has passed its peak, and that many deaths will still occur until the end of June.  

Figure 1: Baseline estimate for COVID-19 in Italy until the end of June 2020

Strengthen scenario: Increased actions bring daily deaths to zero

In Figure 2, we project what would happen if the interventions were 10% more effective or stronger from April 24 onward. The effect is limited over the first few days due to the incubation period. After that, we see a decline in new cases and new deaths. By the end of June under this scenario, there would be days where the death rate becomes very low – ie a rapid drop in fatalities with no change in COVID-19's CFR, herd immunity or available vaccinations. Overall, we would expect around a 9% decrease in deaths from the baseline.

Figure 2: Change in new cases and deaths with a 10% improvement in intervention strength for Italy

Weaken scenario: Increased hospitalisation and mortality

As lockdowns and social distancing timeframes expand from weeks to months, the number of daily positives and deaths begin to diminish but the economic damage mounts. Governments will be increasingly compelled to relax restrictions, but those changes must be carefully enacted, as our model shows how quickly the negative effects can accumulate. Figure 3 illustrates what happens when the effectiveness of interventions are reduced by 10% after April 24. Similar to when actions strengthen, the effects aren't immediately noticed. However, what can be noticed is the number and rate of deaths that significantly increase week on week, reversing all progress to date, and increasing the overall mortality. In only seven weeks, our projections show an increase of over 45% of deaths from the baseline scenario.

Figure 3: Change in new cases and deaths with a 10% decline in intervention strength for Italy

Variable scenario: Shows the benefits of slow and careful relaxation  

A widely discussed solution is the "variable" solution or a gradual relaxation of restrictions, with flexibility to ramp up should cases spike again. In Figure 4 we show what could happen through the end of December 2020 for Italy if restrictions are relaxed mid-June, allowing a return to normalcy in the summer followed by a recurrence in autumn. We intend to show how the shape of the curve changes along with the degree of restrictions. A peak in the autumn leads to a resumption of restrictions at the start of October, leading to another decrease in deaths by the end of the year.

Figure 4: Increase and decrease in restrictions from April 2020 until the end of December 2020 for Italy

Austria

Baseline scenario

On 25 February, Austria began detecting cases that originated in Italy, setting off a cluster of infections around the country. Restrictions were placed on schools, universities and mass gatherings within days, and by 16 March the country was in full lockdown. Figure 5 shows the impact of these orders on our baseline estimate. By the end of May we expect a large drop in the number of deaths with the current scenario, and by June we would expect to see no more reported deaths.

Figure 5: Baseline estimate for COVID-19 in Austria until the end of June 2020

Strengthen scenario: Limited impact for a country already near the end

Even though current restrictions appear to be achieving favourable results, we project what would happen if interventions were 10% more effective from April 24 onwards (see Figure 6). Again, the impact is limited for the first two weeks and specifically the first few days, due to the incubation period of the disease. We then see a decline in new cases, and deaths drop to zero already within May. This is without a change to the CFR, vaccination program or herd immunity. Overall, we would expect to see a decrease of 5% of deaths from the baseline. It’s possible that this further level of implementation would not be warranted considering the potential minimal benefit.

Figure 6: Change in new cases and deaths with a 10% improvement in intervention strength for Austria

Weaken scenario: Too fast and it negates Austria's improvements

With a relative low number of deaths, there will be political and economic pressure to significantly reduce the strength of interventions. Figure 7 shows no further improvements in death rates when the effectiveness of interventions is reduced by 10% from April 24. Instead, we predict a movement towards a rather stable scenario. The number of new cases and deaths would remain constant until the beginning of June. This would curb the progress that Austria had made and ultimately lead to more overall deaths. It is important, however, to remember that the number of modelled deaths in Austria are far lower than other countries. We project that this would cause an increase in deaths of just below 25% above the baseline scenario.

Figure 7: Change in new cases and deaths with a 10% decline in intervention strength for Austria

A 10% increase in strength of interventions has an exponentially larger benefit to new cases and mortality. Thus, the impact of limiting interventions becomes more severe than a higher case fatality rate (CFR).

Impact of interventions is not linear like the impact of the case fatality rate

While the CFR is a key factor driving deaths, conclusive data on the CFR of COVID-19 has not yet been established and ranges from 0.7% in Germany to 10.8% in Italy. Globally a value of 4.7% has been reported7. This value depends on testing. For purposes of this article, we have selected separate CFRs according to age bands and countries, following the data provided by the Imperial College models4.

CFR is a key factor to consider and the projection of the ultimate mortality depends heavily on it, deaths naturally increase along with a linear increase in CFR. The impact of interventions, however, is not linear. A 10% increase in strength of interventions has an exponentially larger benefit to hospitalisations and mortality. Thus, the impact of limiting interventions becomes more significant than a higher CFR.

Game changers: other factors to consider

What could change our projections? We have only explored the importance of interventions here – they are already in place across the globe, and can be quickly changed by governments. There are five big factors that could change our projections:

  • Vaccination: Finding a vaccine for a new infection is a long process. Some reports are optimistic that millions of doses could be ready by the end of the year. As clinical trials have started there will be challenges and opportunities that this could bring.
  • Medication: There are two options, either finding a new drug to treat COVID-19, or finding another use for a previously marketed drug. Over 500 clinical trials are currently ongoing with various degrees of how and when such drugs could change the hospitalisation duration rate and save many lives.
  • Population-wide immune testing: Population-wide immune response testing will be an essential component for long-term success to understand the level of population infection and immunity
  • Herd immunity: As the percentage of infections and recoveries grow, the susceptible population decreases in a country. At the moment the model assumes that the infection rates are low enough that there is not a material impact from herd immunity. If the infection rates were found to be much higher, with more asymptomatic patients, then this could change our outcome
  • Reoccurrence management: Newly emerging outbreaks will need to be managed tightly. Strategies will be required allowing for proactive contact tracing and early isolation, as well as, quarantine of people potentially infected. A socially accepted and effective contact tracing app could be of great help. Also a focus should be given on reducing and preventing household transmission with an emphasis on the importance of having the infected person quarantined and wearing a mask.

Interventions are still a must and should be relaxed very carefully

Our scenarios lead to some important conclusions:

  • Every country is at a different stage in this crisis, and needs to view it as a marathon, not a sprint.
  • Decisions on altering interventions must be deliberate and carefully considered based on data.
  • If restrictions are lifted too early, there will be exponentially more cases, more hospitalisation and more deaths.
  • A second wave of infections is entirely possible and needs to be tightly managed.

Interventions are not a simple on and off switch. They are impactful changes to the way that we all live our lives. Our interventions extend far beyond social distancing and isolation, they can be more subtle as we look to expand towards contact tracing or the use of apps. Apps and other digital tracking methods can bring privacy concerns. As lockdowns and quarantines continue, people may be willing to trade some privacy for a welcome return to physical freedoms like socialising, travelling and working together.

What is becoming clear, and what we saw through these scenarios, is that repeated strengthening and weakening may be needed to stem the tide of COVID-19. This is not without cost, as fatigue and lower adherence from repeated social isolation is likely to set in. As Europe looks to re-open in the coming weeks, all eyes will be on Austria and Germany who have taken some of the first steps toward a return to normal. A significant second wave of infections could mean longer lockdowns. Before making timing decisions, governors of the worst affected states in the US will surely be looking at how Europe copes with re-opening.

We have shown the effects of interventions, and their projected impact on mortality, and we have given a brief overview of the important game changers that might come in to play. These will be addressed in more detail in a series of papers soon. Our next article will focus on the importance of antibody testing, and its potential for long-term control of the spread of COVID-19. Stay tuned.

Disclaimer

This is a highly simplified model designed to present a range of possible outcomes under different intervention scenarios. The study is meant to spark questions and inform debate for informational purposes  but is not in any way a business model or insurance industry projection that can be relied on . The results presented here should not be regarded as representative of Swiss Re's own internal projections or forecasts, and Swiss Re is under no obligation to update the results presented here.

Contributing editor
Susan Imler, Global L&H Communications

References

  1. European center for disease prevention and control. Coronavirus disease 2019 (COVID-19) pandemic: increased transmission in the EU/EEA and the UK – seventh update. 2019, (2020).
  2. Flaxman, S. et al. Estimating the number of infections and the impact of non-pharmaceutical interventions on COVID-19 in 11 European countries. Imp. Coll. London 1–35 (2020) doi:10.25561/77731.
  3. Zhang, S. et al. Estimation of the reproductive number of novel coronavirus (COVID-19) and the probable outbreak size on the Diamond Princess cruise ship: A data-driven analysis. Int. J. Infect. Dis. 93, 201–204 (2020).
  4. Ferguson, N. M. et al. The Global Impact of COVID-19 and Strategies for Mitigation and Suppression. Imp. Coll. COVID-19 Response Team 1–19 (2020).
  5. Guan, W. et al. Comorbidity and its impact on 1,590 patients with COVID-19 in China: A Nationwide Analysis. European Respiratory Journal (2020).
  6. The Economist. Tracking covid-19 excess deaths across countries. https://www.economist.com/graphic-detail/2020/04/16/tracking-covid-19-excess-deaths-across-countries?fsrc=newsletter&utm_campaign=the-economist-today&utm_medium=newsletter&utm_source=salesforce-marketing-cloud&utm_term=2020-04-16&utm_content=article-link-4 (2020).
  7. Omer, S. B., Malani, P. & Del Rio, C. The COVID-19 Pandemic in the US: A Clinical Update. Jama (2020) doi:10.1001/jama.2020.5788.

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