Across Canada, thousands of new coronavirus cases are reported each day, as the COVID-19 pandemic has taken a hold on everyday life.
But does the official case count actually paint the true picture of the pandemic and show how widespread the disease really is? Experts say not quite.
“The daily numbers of new cases are a significant underestimation of real COVID prevalence,” said Dionne Aleman, professor of industrial engineering at the University of Toronto, in an interview with Global News. Aleman has worked on COVID-19 modelling predictions and planning.
Most people who get COVID-19 are either asymptomatic or have mild symptoms, so they don’t get tested, while others choose not to take a test for one reason or another.
“There are a lot of disincentives for people to go and get tested, and that’s not even counting the fact that the rules for who is even eligible to get tested are constantly changing and shifting,” Aleman said.
Limited testing capacity and access to healthcare also make it harder to know how much of the virus is actually out there.
The United States has by far the world’s highest coronavirus caseload, having surpassed 27 million cases. However, that number does not tell the whole story.
Modelling done by researchers at Columbia University in New York City estimates that more than 120 million people in the U.S. have already been infected, which is almost five times more than that reported.
This model has not been published yet or peer reviewed, but was shared exclusively with National Public Radio.
How did the researchers come to this conclusion?
In an interview with Global News, Jeffrey Shaman, lead researcher and professor of environmental health sciences at Columbia University, said his team developed a system for simulating, projecting and studying the viral dynamics of SARS-CoV-2, and ran this mathematical model in conjunction with actual observed cases, deaths and the movement of people.
“We found that, right now in the United States at least, around one in four infections is being confirmed,” Shaman said.
However, the average person is infectious for about three and a half days, he said.
“So roughly speaking, we’re talking 12 to 15 times as many contagious persons on a given day as there are confirmed cases.”
Shaman and his team also did similar modelling for China in the early days of the pandemic last year and found that one in seven confirmed cases were being detected before the lockdown. That number later changed to one in three as China ramped up testing.
Globally, there are going to be “large differences” between the documented and undocumented cases, Shaman said.
In Canada, experts estimate a four- to 10-fold higher case count per day.
“It’s hard to put a finger on how much higher actual cases are than reported cases, but 10 times is certainly plausible,” Aleman said.
In July last year, a study that was not peer-reviewed estimated that the number of infections in British Columbia was eight times more than the confirmed cases.
Colin Furness, an infection control epidemiologist and assistant professor at the University of Toronto, said this will vary from province to province, but four times more daily cases would be a safe estimate.
While most health experts and doctors agree that hospitalizations and deaths reflect the “burden of COVID-19,” knowing the actual number of cases can help in the pandemic response.
“If you’re going to control the virus broadly, it’s very important to know how much of it is out there,” Shaman said.
Calculating the true infection rate can also help design vaccination strategies, and better understand how COVID-19 spreads and how dangerous it is, Furness said.
Random sample testing of the population before the vaccine rollout would have been helpful, he added. Furness also recommended surveillance testing of staff at restaurants and grocery stores.
“This is a very different bug if we think the whole population had it and only a very small number have gotten very sick.”
— with files by Global News’ Linda Boyle.