TORONTO -- Since the start of the pandemic, Canadian officials have continuously used the threat of a 鈥渟econd wave鈥� of COVID-19 infections in order to remind people to adhere to public health guidelines.

The term second wave has been used repeatedly by politicians, economists, and medical experts alike to warn the public of the threat of a resurgence in cases if they鈥檙e not careful.

Both Prime Minister Justin Trudeau and Chief Public Health Officer Dr. Theresa Tam have repeatedly cautioned Canadians about an impending second wave with Tam suggesting there was the possibility for an 鈥渆xplosive鈥� second spike in new infections.

So, what exactly constitutes a second wave? And if there is one on the way, can it be prevented? CTVNews.ca spoke to several experts to find out.

WHAT IS A SECOND WAVE?

Epidemiologists have been using the metaphor of waves on the sea to describe the rise and fall in the number of cases, or the 鈥渃urve鈥� of an outbreak, for years.

During the Spanish Flu of 1918, officials documented three distinct waves of illness beginning in March of that year. The second wave of that pandemic, which was far deadlier than the first, hit in the fall of 1918 before it subsided for almost a year and resurged again in the fall and winter of 1919.

Since then, the metaphor has been used on multiple occasions in reference to other influenza outbreaks throughout the 20th century, including more recently during the 2009 H1N1 pandemic.

Steven Hoffman, a professor of global health, law, and political science at York University in Toronto and director of the Global Strategy Lab, said a 鈥渨ave鈥� is an imprecise term that is used colloquially to highlight the overall shape of an epidemic curve in terms of the number of new cases per day.

鈥淭here鈥檚 nothing so precise about it. It鈥檚 more just a helpful communication tool,鈥� he told CTVNews.ca during a telephone interview on Wednesday.

Infectious disease specialist Dr. Isaac Bogoch agreed there is no exact threshold of new daily cases that needs to be reached to be able to determine if a second wave is occurring.

If they are plotted on a graph, for example, Bogoch said the number of new daily infections would be seen rising before peaking and then decreasing again when there are no or few cases for a sustained period of time. The second wave would begin when the cases begin to rise again for continued period.

鈥淚t鈥檚 as simple as that,鈥� he said during a telephone interview from Toronto on Wednesday. 鈥淵ou鈥檙e not going to have an exact definition.鈥�

HOW DO WE KNOW THE FIRST WAVE IS OVER?

Part of the confusion around the usage of the term second wave is determining when the first wave actually ends and a new wave begins. While some countries including Canada, South Korea and Australia saw a fairly obvious increase in new infections that eventually peaked before decreasing again, that鈥檚 not always how an outbreak develops.

In the United States, for example, there hasn鈥檛 been a dramatic drop in new cases that marks a clear end to the first wave. Since the outbreak began, the country has seen more of a bumpy curve with periodic spikes and no sustained period with few or no cases. Since mid-June, the U.S. has had some of its highest number of recorded cases leading some to believe they鈥檙e experiencing a second wave.

However, American health officials including the country鈥檚 top infectious disease specialist Dr. Anthony Fauci have been reluctant to label it as such, because the curve of news cases never flattened. 

鈥淵ou鈥檙e sort of seeing the first wave rolling into the second wave, a much bigger one right now,鈥� Hoffman said. 鈥淚 mean, did they ever get through the first wave? Not really.鈥�

Bogoch said he doesn鈥檛 think the semantics really matter because, whether it鈥檚 a continuation of the first wave or a second wave, an increase in cases should elicit the same response.

鈥淚s this a second wave or a blip? Or a spike in our first wave? Like, who cares? Really,鈥� he said. 鈥淭here might be some academic epidemiologists that don鈥檛 agree with me on that, but that's OK. From a practical standpoint, it doesn鈥檛 matter.鈥�

Bogoch said countries should focus on whether they have a population susceptible to the virus and if they have good policies in place to prevent further spread.

WILL THERE BE A SECOND WAVE?

No matter the label, Hoffman says a second wave of infections will likely hit Canada.

鈥淲e鈥檙e almost certainly going to get it because there鈥檚 such infectious potential out there, there's so much of this virus that is present around the world,鈥� he said.

Save for a few recent spikes in some parts of the country, Bogoch said Canada is currently seeing low transmission overall, which he said indicates the first wave is coming to an end in this country.

As for the prospect of a second wave on its way, Bogoch said he agrees it will very likely arrive in Canada in the fall. He said a number of factors may contribute to a resurgence in cases at that time, including schools and workplaces reopening, and cooler temperatures keeping people indoors more.

鈥淲e鈥檝e really learned a lot about how this virus is transmitted and where it's most likely to be transmitted,鈥� he said. 鈥淪o any settings where people are in an indoor environment in close proximity for prolonged periods of time, we know that that鈥檚 a perfect setup for this virus to be transmitted.鈥�

Hoffman added that it鈥檚 really anyone鈥檚 guess when the second wave will come, however. He said it will be dependent on public health guidance and people鈥檚 adherence to those policies in the coming weeks.

鈥淭here鈥檚 nothing stopping a second way from happening much earlier if we鈥檙e not careful,鈥� he said.

CAN A SECOND WAVE BE PREVENTED?

While both Hoffman and Bogoch are confident a second wave will likely hit Canada, they both said the severity of that surge can be mitigated with the proper response.

Bogoch cited South Korea as an example of a country that had a dramatic spike in cases early on, but they were able to largely suppress it through the extensive use of testing, isolating, and contact tracing.

When cases numbers began to creep back up again in June, South Korea halted further relaxation measures and relied on a program of aggressive tracking, tracing, and testing for the virus to bring the numbers down again in what the government described as the country鈥檚 second wave.

Bogoch said that type of speedy reaction will be needed to tamp down on localized outbreaks if Canada wants to prevent a wave of new infections.

鈥淚t鈥檚 like a game of Whac-A-Mole,鈥� he said. 鈥淚nfections are going to pop up and we鈥檙e going to have to smack them down and the key thing is we have to rapidly identify them and quell those outbreaks as quickly as possible before they morph into larger outbreaks.鈥�

Hoffman said, without the development of a vaccine or treatment for COVID-19 or a scenario where everyone contracts the virus and there is herd immunity, Canadians will have to continue to physically distance from each other, wear masks, and practice good hygiene to avoid devastating second, third, or even fourth waves of infection.

鈥淲e need to be ready for when that second wave likely comes and ideally be able to react and stop it so fast that it hardly look like a wave at all,鈥� Hoffman said.