Researchers are finding mounting evidence that asymptomatic COVID-19 carriers are “driving” the rapid spread of the virus around the globe — contradicting what Canadian officials were saying just weeks ago.
Researchers are finding mounting evidence that asymptomatic COVID-19 carriers are “driving” the rapid spread of the virus around the globe — contradicting what Canadian officials were saying just weeks ago.
At the end of January, Canada’s chief public health officer, Dr. Theresa Tam, told the House of Commons health committee that based on what is known about past coronaviruses, asymptomatic transmission is a “rare event.” In fact, she said, epidemics are not driven by that kind of transmission.
A few days after that, Health Minister Patty Hajdu echoed Tam in an interview on CBC Radio’s The House:
“The best evidence around the virus that we have is that the virus is not contagious when people are not symptomatic.”
But a growing body of research indicates they were wrong. In fact, people don’t have to appear ill at all to infect others.
Jeffrey Shaman, a professor of environmental health sciences at Columbia University in New York, says he is frustrated when people deny that asymptomatic spread can happen.
“We have so much evidence that that is going on,” he said. “It’s ridiculous.”
It remains unclear if understanding the threat earlier might have affected policy. Had the threat been fully realized, different decisions might have been made regarding travel restrictions, quarantines and physical distancing.
Asymptomatic patients among COVID-19 caseload: studies
Shaman and other researchers argue that even two months ago, officials like Tam and Hajdu should have been more open to the possibility of asymptomatic transmission, considering by that point there was a flurry of research being undertaken by scientists racing to understand how the virus was spreading so fast and far. Many of those researchers suspected asymptomatic transmission.
As the results of much of that research are so new, some of the findings have yet to be peer-reviewed. But, they appear to point in one direction.
“That is what our Science paper suggests, that it is undocumented infections that are driving it,” said Shaman. “They’re silent spreaders; it’s ste