COVID-19 virus SARS-CoV-2

North American Epidemiology


The evolution of COVID-19 epidemiology in North America between March 01, 2020 and August 15, 2021 expressed as the number of confirmed positive cases per 100000 per Km2 of significant population density area. In the USA (continental US only excluding Alaska and Hawaii) and Canada only epidemiologically significant territory with population density > 5-10 individuals/Km2 were included in the analysis. Note that until February 2021 SARS-CoV-2 virus behaved as one panmictic population unit throughout the entire continent regardless of non-pharmaceutical intervention measures implemented in either country. The US epidemiology changes after the murder of George Floyd on May 25, 2020 due to Black Lives Matter organized protests which resulted in super-spreading events across the US. It was estimated that about 21 million people attended these protests by mid June. This was reflected in the substantial increase in incidence of reported COVID-19 cases.

About sixty percent of the US population became exposed to the SARS-CoV-2 virus sometimes between the holidays and began mounting its natural immune response to the pathogen. The observed dip in reported cases after December 20, 2020 likely reflects the slow down of COVID-19 testing between the holidays, however significant drop in the US and Canadian COVID-19 incidence was observed on January 10, 2021only after the US population reached its herd immunity threshold for the strain of the virus responsible for the US and Canadian second wave. Interestingly, the COVID-19 incidence in Canada begins to follow the much larger US population trend. Nevertheless, by May 16, 2021 only 35% of the Canadian population was exposed to the virus suggesting that Canada can expect more significant waves to come.

The Canadian COVID-19 incidence between March 22, 2020 and June 6, 2021 plotted together with its corresponding infection fatality ratio (IFR). Notice the COVID-19 prevalent mortality gradually dropping throughout the pandemic as the Canadian population continues its exposure to the virus and begins mounting its immune response. 

At the beginning of the pandemic the apparent COVID-19 mortalities appeared very high due to a number of unrelated factors such as, the unfamiliarity with the novel disesease resulting in late diagnosis or misdiagnosis of COVID-19, lack of initial testing (this artificially diminished the equation denominator resulting in large mortality value), in addition to some initial mishandling of severe cases due to overwhelming of the medical system. This region of the graph (blue dots) by no means reflects the true morbidity of COVID-19.

The Canadian IFR continues fluctuating below 0.2% while continually dropping throughout the second wave.

The US COVID-19 incidence between March 22, 2020 and June 6, 2021 plotted together with its corresponding infection fatality ratio (IFR). Like the Canadian trend pictured above, the US COVID-19 prevalent mortality is seen gradually dropping throughout the pandemic as the large US population continues its exposure to the virus and begins mounting its natural immune response. 

The US prevalent COVID-19 infection fatality ratio (IFR) remained fluctuating around 0.16% throughout much of the pandemic with the exception of the first wave, which was followed by the Black Lives Matter protests (blue dots in the figure above). At the beginning of the pandemic the apparent COVID-19 mortalities appeared very high due to a number of unrelated factors such as, the unfamiliarity with the novel disesease resulting in late diagnosis or misdiagnosis, lack of initial testing in addition to some initial mishandling of severe cases due to overwhelming of the medical system. This region of the graph (blue dots) by no means reflects the true COVID-19 morbidity.

Data: WHO weekly reported SARS-CoV-2 virus positive cases.