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Contextualizing COVID-19: What We Know and What We Can Expect

COVID-19 Virus (Coronavirus) Molecule Diagram
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Analysis of 2009 and 1918 pandemics and impact of temperature and humidity on COVID-19 predict viral spread to halt in June/July but second wave possible in fall/winter. Prolonged viral shedding after symptom resolution leads to long infectious period. But early data show that reinfection is less likely, suggesting herd immunity possible. Spike protein is good target due to slower mutation rate.

COVID-19 Has Already Outpaced Prior Coronavirus Outbreaks Due To Long Infectious Period Even Following Resolution Of Symptoms

The current COVID-19 pandemic represents the third and most severe outbreak of coronavirus since the turn of the century. The 2002-‘03 spread of SARS lasted ~7 months and included >8,000 confirmed cases of infection and 774 deaths across 26 countries. The more recent outbreak of MERS in 2012 was much narrower in scope and initially included 55 confirmed cases of infection in 2012 and an additional 186 cases in the 2015 South Korean wave. Despite the notably lower rate of human-to-human transmission, ~35% of people diagnosed with MERS died during that outbreak. Both prior outbreaks were self-limiting, but we note that the ongoing COVID-19 pandemic has rapidly surpassed SARS and MERS.

1918 And 2009 Influenza Pandemics Suggest New Infections Will Subside in July/August But May Recur Depending On Effectiveness Of Current Interventional Strategies And Development Of Herd Immunity

Both major outbreaks of influenza in 1918 and 2009 spanned 12+ months. The 1918 pandemic alone is thought to have killed ~1-6% of the global human population (over 25 million people) and the CDC estimates the H1N1 flu in 2009 claimed ~150,000-500,000 lives globally. We note that both pandemics demonstrated a consistent outbreak pattern wherein the first wave of infections subsided after ~3-6 months and were followed by a larger second wave (2009 pandemic) and even third wave (1918 pandemic) as the seasons transitioned again to fall/winter.

Though local responses to the current COVID-19 pandemic have varied by country, we believe the extent to which the virus will surge again in the fall will depend in many respects on the effectiveness of current interventional strategies. Some cities and countries have implemented social distancing and shelter in home (Milan, Paris, Israel, New York, San Francisco, Wuhan) or mandatory stay-at-home policies to slow the spread of the virus.

New Data Suggests Viral Transmission Is Boosted By Cooler Weather With Lower Humidity

Recent data shows that most of the outbreaks fall within a relatively narrow latitude band (30-50N) and have similar weather conditions (~40-70°F and absolute humidity of ~4-9 g/ m3 ). Using previous pandemics as a guide, we anticipate a halving of the current outbreak over the coming summer months as average temperatures reach 80°F+ and absolute humidity increases.

Recent work out of MIT suggests that humidity’s impact on viral transmission may be marginal until as late as June or July for New York, Seattle and most of North America and Europe given the lower rise in absolute humidity (relative to parts of Asia that see a rapid increase during monsoon season).

Infectious Period Lasts Even After Resolution Of Symptoms – Requiring Longer Quarantine Times

Studies out of Wuhan in hospitalized patients reveal that onset of symptoms (typically shortness of breath) occurred 4-9 days after time of illness, ICU admission 8-15 days after time of illness, and death 15-22 days after time of illness. Duration of viral shedding ranged from 8-37 days (median of 20 days in survivors). This suggests that the infectious period lasts even after resolution of symptoms.

Clinical Course Of The Virus: What Does Early Data Show Out Of China, Italy And US?

Based on early outcome data, Italy has a higher mortality rate than the U.S. or China. This appears to be based on a combination of an older population that have a high rate of antibiotic resistance and where ~28% are smokers. More so, the rapid rise in cases overwhelmed Italy’s healthcare system leading to worse outcomes. In the U.S., contrary to the common misconception that COVID-19 is a disease of the elderly, data from the CDC show that nearly 40% of cases sick enough to be hospitalized were age 20 to 54. Additionally, 30% of cases requiring admission to the ICU were age 20 to 54.

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