On: 1918 Spanish flu pandemic—historical account, parallels to today, and lessons
Date: 17 April 2020
Historian and author of “The Great Influenza: The Story of the Deadliest Pandemic in History”.
- 1918 Spanish Flu pandemic killed between 50-100 million people (out of 1.8 billion people).
- Three waves (spring 2018, sep-dec 2018, spring 2019): second wave 2/3 of fatalities.
- Different from common flue in the way it afflicted young people with strong immune systems.
- Common flu: mortality is U-shaped -> affects the young and the old / immunocompromised.
- Spanish flu: mortality is W-shaped -> also affects people in their 20s and 30s (peak age 28 years old) with strong immune systems.
- Strong immune system response = more damage to the lungs.
- High mortality (case mortality of about 2% in the Western world), as virus spread rapidly.
- Virus bound to upper respiratory tract cells, making it easy to spread.
- Virus bound to lower respiratory tract cells, causing viral pneumonia.
- Some immunity across waves of infection, but virus may have changed over time:
- Exposure to first wave infection: largely immune against second wave.
- Exposure to first / second wave infection: not necessarily immune against third wave.
- May be due to antigenic drift in the virus (genetic variation).
- Sub-optimal government reaction may have made things worse.
- Only thing we learn from history is that we learn nothing from history.
- Government spread misinformation, eroding societal level of trust.
- 1918 Spanish Flu and COVID-19 – similarities:
- Both are respiratory viruses that jumped from animal to human.
- Both bind to upper and lower respiratory tract cells.
- 1918 Spanish Flu and COVID-19 – differences:
- Spanish Flu – H1N1 virus; COVID-19 – corona virus.
- COVID-19 takes longer to develop in the body than Spanish Flu and much longer to pass through.
- Combined with social distancing, will take longer for COVID-19 to pass through the community (Spanish Flu waves second wave was about 14 weeks).
- COVID-19 and the common flu – making the wrong fatality rate comparison:
- COVID-19 fatality rate may end up being well below 1%, maybe as low as 0.1%.
- People think this is close to the oft quoted fatality rate for the flu of about 0.1%.
- But, for the flu, the 0.1%rate is the case fatality rate.
- For COVID-19, the quoted rate is usually the infection fatality rate.
- Case fatality: fatalities per reported cases of infection.
- Infection fatality rate: fatalities per infected persons.
- The common flu infection fatality rate is not known and likely much lower than 0.1%
- We don’t know how many people actually get infected with the flu.
- Many people that are infected are immune and will not show up in denominator.
- The infection mortality rate of the flu is likely an order of magnitude below 0.1%.