Tracing COVID Sources as Canada Starts to Open its Borders (Part 2 of 2)

Catherine Harmel-Tourneur


September 1, 2021

mod Air Canada B787 9 over the Rockies scaled

In the first part of this detailed analysis, DKMA established that a mix of airlines had carried passengers with COVID19 into Canada last Spring, but that some source airports were much more problematic than others. In this second part, we look at the Canadian gateways that were most affected, and examine two hypothetical scenarios of how conditions might change by December – and it doesn’t look ideal. 

International flights were allowed to land at only four Canadian airports* when the data for this study was collected (April 13 to July 31). They were:

  • YUL Montréal-Pierre Elliott Trudeau
  • YYZ Toronto Pearson
  • YVR Vancouver
  • YYC Calgary.

During that period, 75% of the 892 COVID cases identified were concentrated in Eastern Canada. However, Calgary Airport had the greatest share of COVID affected flights (at 18%, see maps below), or almost one in five, with AMS, DFW and DEN accounting for 70% of the cases.


During the period of analysis, case numbers were highest in Toronto and Montreal (above), but in terms of proportion of flights Calgary was worst hit (below).

dkma canada airport case proportion From early April, thanks to the emergence of the Delta variant from India, COVID cases were increasing and this prompted the government to act. Starting April 18 (corresponding to week 17 in the charts below) direct flights from India were banned.

Subsequent to this action, the number of affected flights diminished (both in volume and percentage of flights) and this situation remained fairly stable at 56 flights on average until week 28 (starting July 4). Since then, the number of weekly affected flights has more than doubled to an average of 122.

In parallel, the share of affected flights has also increased, averaging 14.6% during the last three weeks (29-31), up from around 9% in prior weeks. We don’t have figures at a Canadian level but on August 12, the Regional Direction of Public Heath of Montreal indicated that about a third of all COVID cases were linked to international travel. It is also interesting to note that starting July 5, fully vaccinated travelers were no longer required to quarantine or complete a day-8 test.


Weekly affected flights fell after week 17 but not for long, while the share of infected flights also soared.

Unsurprisingly, when the Canadian government announced that it planned to re-open its borders, a number of carriers introduced additional flights. Both the US and the rest of the world are currently expected to have flight levels in December 2021 close to those in December 2019.

Fourth Quarter Bounce – for Flights and COVID Cases

Since the pandemic started, we have grown accustomed to carriers typically scaling back their flight schedules as the departure date gets closer. Even if this happens, it is safe to assume that, if all international borders are re-opened by September 7, flight activity during Q4 will be the highest of the year.

With the Delta variant currently the dominant strain, coupled with the re-opening of international borders and increased scheduling, it is likely that the number of affected flights will increase despite the tight entry measures accompanying the re-openings. While this seems probable, it is impossible to know the number of cases, their origin and which Canadian regions will be most impacted.

In spite of the uncertainty, a simple ‘what if’ scenario was prepared based on the following:

  • We estimated the number of cases in December 2021 and compared them to (a) the last three weeks in July and (b) April 13 to July 31.

  • To estimate the cases in December we assumed that (1) there would be no change in the currently planned airline flight schedule; and (2) we factored in two ‘contamination’ levels: one lower, which corresponds to the percentage of affected flights between April 13 and July 31, and a higher level corresponding to weeks 29-31.

  • For ease of comparison all figures in the tables below are on a daily basis.


As expected, the numbers of cases (under both scenarios) increase to unprecedented levels, in the worst case by a multiple of ten (compare the red box totals in the two tables above). If indeed Canada does head in that direction, the government might react, for example by closing the borders again in an effort to keep the epidemiological situation under control.

If this happened, it would be a step back for this industry and while there is a lot of uncertainty surrounding these scenarios, they highlight the challenges ahead for the commercial aviation industry as it tries to rebound.

* Starting August 9 international flights have been permitted to land at five additional international airports: Halifax, Quebec City, Ottawa, Winnipeg and Edmonton.

[Part 1 was published on August 25, 2021. Lead image courtesy of Air Canada.]