COVID | ESG & Climate Change | US
Social distancing is currently considered one of the most effective mechanisms to control COVID-19. But what can history tell us about how well this type of nonpharmaceutical intervention works? Looking at US cities hit by the Spanish Flu of 1918-1919 – the deadliest pandemic on record – a 2007 paper funded by US Centers for Disease Control and Prevention reveals clear findings: social distancing is a good idea. Specifically, some combination of quarantines, public gathering bans and school closures were effective in reducing the duration and scale of fatalities. Importantly, the results were best when interventions were implemented early and for a sustained basis even when infection rates were falling.
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Social distancing is currently considered one of the most effective mechanisms to control COVID-19. But what can history tell us about how well this type of nonpharmaceutical intervention works? Looking at US cities hit by the Spanish Flu of 1918-1919 – the deadliest pandemic on record – a 2007 paper funded by US Centers for Disease Control and Prevention reveals clear findings: social distancing is a good idea. Specifically, some combination of quarantines, public gathering bans and school closures were effective in reducing the duration and scale of fatalities. Importantly, the results were best when interventions were implemented early and for a sustained basis even when infection rates were falling.
Why Deploy Non-pharmaceutical Interventions:
Although unlikely either to prevent a pandemic or change a population’s underlying biological susceptibility to the pandemic virus, nonpharmaceutical interventions could be critical in delaying its impact. They can lessen both the overall attack rate and its peak – in effect, helping to reduce the total numbers of deaths. Additionally, by impeding the impact, such interventions also alleviate the burden on healthcare stystems and provide extra time for production and distribution of vaccines and antiviral medication.
The Set-Up
Data
The researchers obtained mortality data (pneumonia and influenza deaths) from the US Census Bureau’s Weekly Health Index for 43 cities in the United States from 8 September 1918 to 22 February 1919. They captured information about nonpharmaceutical interventions implemented by reviewing archival newspapers for each city and via the available state health reports.
Estimation
The researchers estimated the onset of influenza in a particular city as either the day of the first reported case or the calendar day of the first recorded death (related to pneumonia or influenza) minus 10 days, whichever was earlier. Later, they compared this figure with the estimated baseline of median deaths from pneumonia and influenza from the period 1910-1916 to arrive at weekly excess death rates (EDR). The authors then estimated the impact of nonpharmaceutical interventions in reducing the EDR (10 days after the actual date of implementation).
The main observed nonpharmaceutical interventions:
• Isolation and quarantine
• School closure
• Public gathering cancellations
They then test how the duration, timing, and combination of nonpharmaceutical interventions affected mortality (EDR) by performing analysis of variance (ANOVA).
3 Key Findings
The Timing of Intervention Matters
Figure 1 shows, on average, that those cities which implemented nonpharmaceutical interventions earlier (i.e New York City) were slower to reach peak mortality rates. Also, these cities had a lower peak mortality rate and total mortality. This result was also statistically significant (P<0.05) with strong Spearman’s rank correlation.
Integrated Interventions Are More Effective
The study found that layered (combined) nonpharmaceutical interventions – such as implementing both school closures and quarantines – generally had a more statistically significant association on weekly EDR than individually performed nonpharmaceutical interventions. Specifically, combinations including school closure and public gathering bans appeared to have the most profound impact (i.e. they had the lowest P values, most being P< 0.001). The case study of New York City shows that it reacted earliest to the influenza crisis and rigidly enforced the application of compulsory isolation and quarantine procedures. Its cumulative mortality burden was 452/100,000. Meanwhile, St Louis, which implemented the strategy later but adopted a layered approach (school closure, cancellation of public gatherings and isolation), had a better outcome (cumulative EDR=358/100,000 population).
Both Longer Duration and Consistency in Public Health Policy is the Key For Lasting Results
There was a statistically significant relationship between increased duration of nonpharmaceutical interventions and a reduced total mortality burden (Spearman r=−0.39, P=0.005). Pittsburgh relative to Denver had more total EDR and the culprit was a duration of intervention that was 3x smaller (Figure 3).
Denver, despite having relatively lower EDR, experienced dual peaks. The authors found that many cities (including Denver) that experienced two peaks of influenza mortality were those that were inconsistent with their policy (reactive to death toll). They found, among the 43 cities, that no city had a second peak if their first set of interventions were still intact. This indicates that to have a consistent reduction in the death rate deactivating public policy as a reaction to falling death rates is a dangerous idea.
The Bottom Line
It is clear that enacting early, sustained, and combined nonpharmaceutical interventions worked in 1918. And it’s a good bet they will work now to combat Covid-19. Societies are more connected, which means the implementation of interventions should be more coordinated. But with conspiracies theories and misinformation running rampant on social media, it’s anyone’s guess as to whether government-implemented interventions will be observed.
Mehdi is a research analyst at Macro Hive. He’s currently pursuing an MSc in Finance & Investment at Nottingham University Business School and he is a CFA level 3 candidate. Mehdi has previously pursued roles as an Equity Research Analyst, Junior Economist & in Proprietary Trading.
(The commentary contained in the above article does not constitute an offer or a solicitation, or a recommendation to implement or liquidate an investment or to carry out any other transaction. It should not be used as a basis for any investment decision or other decision. Any investment decision should be based on appropriate professional advice specific to your needs.)