A new study suggests that over 100,000 people in the US were infected with Covid-19 by early March – a time when there were only 1,514 confirmed cases and 39 deaths officially reported in the country.
Researchers are still trying to piece together the timeline of how Covid-19 took the world by storm. It currently appears that the first confirmed case of a Covid-19 infection in the US was on January 20 after a Chinese national traveled to Washington State from Wuhan. It was believed that the infection slowly burned through the US in February with just a few thousand cases before rapidly increasing in early March and reaching 100,000 cases towards the end of the month. By the last week of April, the US reached 1 million confirmed cases.
However, this new research paints a slightly different picture. While current figures suggest the US reached 100,000 confirmed cases around March 27, this new modeling says the country had hit 100,000 cases back by early March instead.
Scientists at the University of Notre Dame in Indiana used a simulation model to predict how many transmissions of Covid-19 there were between January 1 and March 12 using data reported by Johns Hopkins University on the number of confirmed cases and deaths, asymptomatic infections, case-fatality rates, and local transmission. The study was published in the Proceedings of the National Academy of Sciences.
Their findings suggest that the number of Covid-19 cases started to rise in the second half of February, unlike previous research that suggested the middle of March was the decisive time.
"We weren't testing enough," Alex Perkins, lead study author and infectious disease epidemiologist at the University of Notre Dame, said in a statement. "The number of unobserved infections appears to be due to very low rates of case detection during a critical time, when the epidemic was really starting to take hold in this country."
However, the researchers say there are a number of study limitations that should be acknowledged. Primarily, the model assumed the number of infections rose with exponential growth, which might not necessarily have been the case. Also, the study did not take into account data on international air travel, which might have swayed the results. In other words, the modeling might have missed a number of important factors.
Nevertheless, the researchers argue their modeling could help to explain why the US has been hit so hard compared to most other countries. For context, the US currently has 5.7 million cases, while the next highest numbers are in Brazil at over 3.6 million cases, India at over 3.1 million, Russia at 959,000, and South Africa at 609,000.
“We look at the United States now and compare it to other countries like South Korea or Germany, New Zealand or Vietnam, any number of countries who have done a much, much better job controlling transmission. The key differences really come down to the time period we examine in this study,” explained Perkins.
“Those countries had adequate surveillance up and running at that time, whereas we show that throughout most of February the United States missed the vast majority of infections that were already out there,” he added. “This particular timeframe that we focus on is really important for figuring out how we got here in the first place.”