U of T news
  • Follow U of T News

Distancing, testing and tracing key to controlling COVID-19 this fall: U of T epidemiologist

Ashleigh Tuite, an assistant professor at U of T’s Dalla Lana School of Public Health, says it's "extremely likely" we will see a resurgence of COVID-19 in Canada, but the timing and severity is difficult to predict (photo by Nick Iwanyshyn)

The novel coronavirus isn’t so novel anymore.

As the global COVID-19 outbreak reaches the half-year mark, more than 10 million people have been infected and more than half a million have died, including about 8,600 in Canada.

While the epidemic curve appears to be falling in Canada, infections are surging at an alarming rate in many other countries.

Earlier this year, Ashleigh Tuite, an epidemiologist and assistant professor at the University of Toronto’s Dalla Lana School of Public Health, created models of the outbreak with colleague Professor David Fisman. At the time, they predicted that social distancing would be required for months, not just weeks, to flatten the curve.

U of T News writer Geoffrey Vendeville recently checked in with Tuite to get her take on what we have learned about the disease over the past several months, what we still don’t know and whether we will face another wave in the near future.

In your view, how likely is it that we will experience another wave?

I think it’s extremely likely that we’ll see resurgences of COVID-19. A large proportion of the population remains susceptible to infection. Population immunity remains well below the levels needed for herd immunity, which would prevent subsequent waves of infection (assuming that immunity is long-lasting).

The timing of these resurgences and how big they’ll be is less predictable. It will depend on a number of factors including: seasonal effects; how well we continue to adhere to protective measures, including physical distancing and wearing masks indoors when distancing isn’t possible; and our public health testing and tracing strategy.

If we have a strong public health response focused on rapid testing, contact tracing and isolation of cases when case counts remain low, we should be able to control small flare ups and prevent large epidemic waves. If we don’t have those systems and processes in place, we’re going to be in for a much more difficult time.

The last time we spoke, you said it remained to be seen whether the changing of the seasons would affect the virus. Do we have a better idea now if the virus is seasonal?

The unsatisfying answer is we still don’t really have a good answer. It’s difficult to conclusively determine if there are seasonal patterns for a virus that has been circulating for less than a year in humans.

Other coronaviruses do display seasonality and there is some research that is suggestive of seasonal effects for SARS-CoV-2. A recent analysis led by a team of researchers from St. Michael’s Hospital and the University of Toronto suggests that seasonality likely plays a minor role in the epidemiology of COVID-19.

One aspect of seasonality that does seem to be helping us in Canada is the tendency to spend more time outdoors with the warmer weather. We’ve learned that the virus spreads more easily in indoor settings, so spending more time outdoors is likely contributing to an attenuation of spread.

Of course, the flipside of this is that with the cooler weather in the fall, outdoor activities and restaurant patios are going to be less attractive, and we’ll have to strategize about how to spend time indoors while minimizing risk of infection spread.

What are some things we’ve learned about the virus that surprised you?

We knew early on that COVID-19 has what we call an “over-dispersed” basic reproduction number. This means that a small number of cases transmit to many others (super-spreader events), while most cases transmit much less.

People have been collecting data on super-spreader events and identified some important commonalities: a lot of these events happen indoors, in crowded spaces and in situations where people are close contact with others.

This had led to the identification of the so-called “three Cs”: closed spaces, crowded places and close contact situations. Avoiding the “three Cs” seems to be a very good approach for avoiding situations where super-spreader events are likely to occur.

What are some important questions that we still don’t have an answer for?

A big unknown continues to be the importance of children for COVID-19 spread. Symptoms of COVID-19 infection in children tend to be milder, so they’re less likely to seek testing or medical care.

We’re still trying to understand if children are as susceptible to infection as older people. The challenge we face is that, in many places, children have been out of school for the past several months, so they don’t have the contact patterns they’d typically have when they’re in school. When children are at school, compared to other age groups, they tend to have contacts with more people and with more people of different ages.

We don’t know if we’re seeing fewer infections in children because they’re not mixing in the ways they normally do, or if they’re protected from infection. Understanding the role of children is going to be important as we start thinking about how to reopen schools in the fall.

The virus appears to be spreading like wildfire in the southern hemisphere and some parts of the U.S. Why?

Not responding quickly or strongly enough early on, when initial spread was first recognized, and opening up prematurely, without adequate alternate measures in place to control spread after lifting lockdowns, seem to be common themes in places that are currently struggling with control.

Unfortunately, we can’t use magical thinking to make COVID-19 go away – there needs to be a plan in place as communities open up. In places where testing and tracing capacities aren’t sufficient, other measures, like mandatory use of masks indoors and physical distancing, need to be used.

Your research suggests that if physical distancing restrictions are relaxed without better contact tracing or testing, infections will surge. Are we any closer to meeting the standard for tracing and testing?

We’re getting there. The province’s labs have increased the number of COVID-19 tests they can perform each day, which is crucial for making sure that we’re finding cases. Ontario also recently announced they’re in the process of replacing the data management system used for tracking COVID-19 case information.

One of the issues with the current system is long lags between a person getting tested and their positive test result being communicated to a public health unit. Case notification and contact tracing can’t start until local public health units have that information. COVID-19 spreads very quickly, so we need the testing and tracing system to be even faster to interrupt chains of transmission.

One area that has received less attention is how we are supporting those who need to isolate. If we are asking people to stay home for 14 days, we need to make sure they can they have access to food, medicine, accommodation, etc. and that they aren’t putting their jobs at risk.

As we open up more, and more people are working outside of their homes, ensuring that we have those supports in place is going to become more crucial. We want and need people to get tested and isolate if they’re infected, and we can’t expect them to do that if the cost of doing so is the possible loss of income or employment.

What are your initial impressions of the soon-to-be-released COVID Alert app, backed by the federal government?

A contract tracing app could be a useful tool to speed up the contact tracing process, but is not going to replace the role of contact tracers. The usefulness of the app is going to depend on how many people download it, but if it can help identify contacts of cases, and that information is used in a way that allows these contacts to get the information and support they need in a timely manner, then that’s a good thing. Since this is the first time using such a tool, it will be crucial to monitor and evaluate its performance.

What guidance do you have for us all as we try to avoid another wave and prolonged lockdown?

Keep up with the hand hygiene, mask wearing, physical distancing and other behaviours that minimize spread as best you can. If you have symptoms of COVID-19, self-isolate and get tested. The cumulative effects of these measures can have a large impact. Things may feel overwhelming; if you’re in a position where you can support or help others, please do. I think we could all use a little extra kindness and patience right now.