Dental Tribune India

Why we need to know ‘Farr Law’ to understand the pattern of epidemics including that of Coronavirus

By Rajeev Chitguppi, Dental Tribune South Asia
March 10, 2020

'Farr Law' - an often ignored law in ­every epidemic hysteria - may throw some light on the pattern of epidemics including that of coronavirus (COVID-19) that is turning into a pandemic. A group of researchers from Shanghai Jiao Tong University School of Medicine, China and Rutgers School of Public Health, NJ, USA have developed a model based on Farr law using the data available on Feb. 8, 2020. They have analysed the data to predict the daily-incidence of 2019-nCoV infection in China, Hubei Province and Wuhan City afterwards. Will this model be accurate in predicting the rise and fall of Coronavirus (COVID-19)?

The novel coronavirus COVID-19, which has originated from China's Wuhan city, is spreading globally and causing a rise in panic among the public.  Since December 2019 and as of 8 March 2020, more than 100,000 cases of COVID-19 (in accordance with the applied case definitions in the affected countries) have been reported, including more than 3,500 deaths.

Even with all the global spread, China still accounts for over 80% of Coronavirus cases and deaths. But we should understand that the COVID-19 cases in China peaked and began ­declining more than a month ago. It's hoped that subsequently, even other countries will follow this same pattern- it's called 'Farr’s Law' - formulated first in 1840 and ignored in ­every epidemic hysteria ever since.

Farr's law states that "epidemics tend to rise and fall in a roughly symmetrical pattern or bell-shaped curve." AIDS, SARS, Ebola — they all followed that pattern. So does seasonal flu each year.

A group of researchers from Shanghai Jiao Tong University School of Medicine, China and Rutgers School of Public Health, NJ, USA have developed a model based on Farr law using the data available on Feb. 8, 2020. They have analysed the data to predict the daily-incidence of 2019-nCoV infection in China, Hubei Province and Wuhan City afterwards.

The researchers found that there are more than 50,000 (37001 on or before Feb. 8) incident cases in China from January 16 to February 15, 2020, and the daily-incidence has peaked in China, Hubei Providence and Wuhan City, but with different downward slopes. They predicted that if no major changes occur, their model shows the daily-incidence of 2019-nCoV to drop to single-digit by February 25 for China and Hubei Province, but by March 8 for Wuhan city. However, predicted 75% confidence intervals of daily-incidence in all 3 regions of interest had an upward trend.

The predicted trends overall match the prospectively-collected data, confirming the usefulness of these "Farr law" models. This study shows the daily-incidence of 2019-nCoV in China, Hubei Province and Wuhan City has reached its peak and was decreasing. However, there is a possibility of an upward trend.

The study 'Trends and prediction in daily incidence of novel coronavirus infection in China, Hubei Province and Wuhan City: an application of Farr law' was posted on medRxiv (as a preprint and non-peer reviewed article) on 23 Feb, 2020.

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