August 30 - September 5 2021
The evolution of the pandemic in the United States during 2020
The United States was the country with the highest numbers of COVID-19 cases and deaths in the world in 2020. 3 waves of the epidemic followed in quick succession: the 1st in the springtime, after the virus first appeared in the country, affecting mainly urban areas; the 2nd during the summer, affecting mainly the south of the country; and the 3rd during autumn-winter, lasting until spring 2021. During this pandemic the country’s health and economic structures have been devastated. Researchers in New York have recently evaluated the consequences of COVID-19 for the United States during 2020.
The researchers constructed an epidemiological model based on different data such as the number of daily cases per region, population movement, and seroprevalence. One of the characteristics of the epidemic is that individuals can transmit the virus while being unaware that they are infected: on a national level, over the total number of tests carried out, 22% on average were positive in 2020, increasing from 11% in March to 25% in December, a change principally due to the increase in testing capacity. However, for the whole of the year 2020, it is estimated that 78,2% of infections in the United States were not documented, and that a third of the American population was infected.
The researchers also estimated the level of the population that was contagious in the United States: it was 0,77% on the 31st of December 2020, equivalent to one contagious person in every 130, a rate that varied greatly according to the city in question. They also estimated mortality rates. At the beginning of spring 2020, the average was extremely high. Over the course of the year, thanks to earlier diagnosis, improved drug treatment and improvements in health care, this level fell, reaching 1,3% by December.
Using this epidemiological model, the scientists were able to quantify different aspects of the epidemic during 2020 and over the 3 successive waves. Despite 20 million reported cases, some 69% of the population had not been infected by the end of 2020. Several factors, including the arrival of the vaccination at the beginning of 2021, enabled the level of people liable to be infected to be reduced.