Learning to Not Fly

Updating my miniseries on flights and exposures through YVR airport in Vancouver. No particular reason

Here’s passengers on flights in and out in and out of Vancouver. Unfortunately the series I get from YVR still ends in November, so we don’t have the full update on how many holiday trips we should be enraged about for those of us avoiding non-essential travel. But we can see that since the arrival of COVID, passenger travel dropped dramatically, then slowly rose in what looks like some combination of a response to lessening restrictions / fears and seasonal patterns.

Speaking to the persistence of seasonal patterns, we can see that August 2019 was the pre-COVID peak for travel, just as August 2020 represents a post-COVID peak for travel. Since then, travel has eased off, which may also reflect the second wave of COVID. The combination of seasonal patterns and renewed COVID concerns might be seen a little more clearly looking at year-over-year passenger patterns in 2020 explicitly compared to 2019. For Domestic passengers, in particular, it looks like travel recovered up to about one-quarter of pre-pandemic levels by August, and pretty much stayed at that level through October, but we may see some evidence of a fall-off in response to the second wave of COVID in November. That said, I have to imagine that once December figures come out, we’ll see a jump in travel, just like in 2019, pointing to the continuing persistence of seasonal patterns.

International travel patterns are different, and more than a little troubling, insofar as they don’t seem to be at all responsive to the second wave of COVID. Though the progress has been much slower than for Domestic travel, International travel just keeps rising back toward historic norms, led, in November, by a sharp jump in travel between YVR and Europe. Yikes.

But how much is all of this jetting around really contributing to the spread of COVID? Unfortunately, we don’t know. Our surveillance system, data consolidation, and transparency game is still pretty weak here in BC. But we can get a very conservative sense of the changing scale of the contribution by just looking at the BC CDC Flight Exposure data (full pdf). There we see a remarkably steady upward rise in flight exposures, despite the leveling off in the overall number of passengers carried. Yikes, yikes!

Once again, posted exposures represent a very conservative estimate of how air travel is contributing to spread of COVID. Obviously, given the combination of asymptomatic cases and our lax testing regime, the BC CDC still isn’t catching all cases. We also don’t get the actual number of confirmed COVID cases per flight, just whether or not there’s been an exposure, and corresponding rows assessed as being at risk. Sometimes there are multiple seat sections, suggesting multiple, and potentially unrelated COVID cases aboard some flights. But the big takeaway is that even before holiday travel, airlines were already jetting around more COVID cases than at any other time in the pandemic.

I’m not sure it’s as useful, but for consistency’s sake, I’ll also post the exposures per 100,000 passengers, which I played around with in my last post. Last time I didn’t include the Miscellaneous International flights, because there weren’t very many, but they included a lot of exposures, and also because I wasn’t entirely clear on the reporting of flights to Mexico, which is where nearly all the exposures occurred. This time I’ll add those flights back in assigned to my best guess of how to combine the data, in part because Mexico seems to be where a lot of non-essential vacationing is occurring. Unfortunately, once again, we only go up to November data. The data highlight just how risky travel to common vacation destinations in Mexico has been, especially back in July, though by November the US and Europe had moved into riskier positions. That said, the chart really obscures the steady rise in risk of exposure for domestic travelers within Canada, still representing most of our travel.

Overall, though data remains poor, we appeared to be flying around an increasing number of COVID cases through 2020, significantly complicating efforts to contain the virus. Particularly worrisome, despite Public Health orders to avoid non-essential travel, lots of people – including politicians and other public figures – took to the skies on recent vacations. For now, folks, it’s probably time to learn to NOT fly. Maybe stay home and watch a video instead?

************* UPDATE January 27, 2021

Still no updated YVR passenger data for December! But lots of discussion about travel restrictions. So I’m posting a comparison of BC CDC flight exposures to overall exposures by month below, running up to January 22 (latest flight exposure notification data). The scales are set to 1 flight exposure = 500 cases reported, though of course I make no claim for direct causality there! The figure merely enables a comparative analysis of trends.

Feel free to grab the spreadsheet behind the figure containing downloaded BC CDC data from Jan 27 here:

Henderson’s Guide to Pandemic History

What will happen when the Pandemic ends?

Will pre-Pandemic patterns, like people moving to Vancouver, go back to normal? Or will small towns, far-flung suburbs, and rural areas see a boost at the expense of cities, reflecting perhaps a new aversion to density and/or embrace of the rise in telecommuting acceptability? (we’ve seen such speculation in certain corners of City Hall).

Or indeed, might we see the opposite? Will people flock to cities like Vancouver as we return to mobility (including newly amped up immigration along with outreach to Hong Kong) and enjoyment of all the urban pleasures we’ve given up during the pandemic?

It’s all speculation at this point. But it’s got me curious about the past. What happened after the 1918-1919 influenza pandemic? And here I struggle with two things: 1) there was a LOT going on during and prior to the 1918-1919 flu pandemic, making it hard to isolate any response, and 2) the census data skips right around the two key years, with timing gaps too large for zooming in.

I can’t fully fix the overlapping events (WWI, and prior to that a big speculative economic crash), but I can kind of get around some of the data limitations of the Census by playing with some historical data sources I’ve been meaning to give more attention, in particular, the brilliant collection of BC City Directories archived by the VPL, including especially Henderson’s City and Greater Vancouver Directories and Wrigley’s BC Directories.

First, a couple of quick notes about the 1918-1919 Pandemic, brought to you by Margaret Andrews (1977) enlightening research in “Epidemic and Public Health: Influenza in Vancouver, 1918-1919” open access in BC Studies vol. 34. According to Andrews, the Pandemic hit Vancouver especially hard relative to other cities in Canada and the USA. It was also very different from today’s Pandemic in targeting mostly young and middle-aged adults.

At the same time, it was similar to today’s Pandemic in arriving across multiple waves, though the first (in 1918) took the greatest toll.

So what can we add by looking at City Guides? Well, we can compare them to Census results to get a more fine-grained sense of how the City responded to and potentially bounced back from the Pandemic of 1918-1919. The guides include, especially, the Henderson’s City of Vancouver Directories and related Wrigley’s Guides (which swallowed up Henderson’s in 1924), all providing listings of businesses (and households) across Greater Vancouver. I estimate the number of listings for each year, folding businesses and households together. While this isn’t a perfect match for population, or even households, it provides a relatively consistent method for a fine-grained look at how Greater Vancouver businesses and households together experienced the concentrated events piling up between census years (more details below!)

What’s our fine-grained examination of directory listings in combination with census data tell us? It appears we really do miss a lot with census data alone, especially between 1911 and 1921, where we saw a gigantic speculative bubble crash in 1913, followed by the Dominion’s entrance into WWI in 1914, and the Influenza Pandemic itself in 1918.

Where Census data from 1901, 1911, 1921, and 1931 make Vancouver’s growth look relatively steady and nearly linear, directory data demonstrate the enormous upset and losses of 1913-1915 in Vancouver, followed by a bottoming out and start at recovery during WWI (when many otherwise unemployed men went to fight in the war), finally interrupted by effective stasis during the Pandemic of 1918-1919. Then boom! Vancouver was off to the races again, climbing rapidly in listings from 1919-1923 and again (jumping different guides & methods) from 1924 seemingly only slowing a bit in 1926. From there, the trajectory of growth seemingly carried right through the beginnings of the Great Depression to 1931, when the next census was carried out.

Is past prelude? If so, Vancouver looks set to recover quite spectacularly from the Pandemic once it ends, as people flock back to the joys of the city. Maybe we’ll get our own Roaring 2020s!

But of course, for now we’re still here in the middle of the damn thing. So I’m still singing “Come On Vaccine.”

You know the tune…

APPENDIX

A couple quick methods notes for my beloved nerds. Historical census data was taken from Norbert MacDonald’s “Population Growth and Change in Seattle and Vancouver, 1880-1960” from Pacific Historical Review 39(3): 297-321 (unfortunately paywalled). MacDonald combines South Vancouver and Point Grey into the City of Vancouver boundaries for 1921, but I believe he considers the populations of these municipalities effectively too low to matter in earlier years. Henderson’s Directories were released on a yearly basis with a pretty standard, two column format, from 1905-1923, and seemingly covered all of Greater Vancouver during this time, with listings showing up in North Vancouver, New Westminster, and Burnaby, for instance (though North Vancouver was sometimes also reported separately). Ads were placed somewhat randomly within the text, rather than as full pages. In 1924, the Henderson directories were absorbed by Wrigley’s directories, using a new three column format (and smaller type) with interspersed full page ads. I attempted to estimate the listings for each year of these two different sources by gathering page numbers for alphabetized listings (of resident households and businesses) and multiplying by an estimate of the number of listings per page, excluding full page ads where possible. I estimated ~95 listings per page for Henderson’s and ~184 listings per page for Wrigley’s, based upon a quick count on what seemed representative pages (the second A listings), but this estimate could certainly use further checking.

Return to the Airport!

A couple of months ago I took the blog for a visit to the airport to check out historical passenger data and see what’s happened since COVID. Today I want to return, both to provide an update and to pull YVR Passenger data (enplaned & deplaned pdf) together with BC CDC Flight Exposure data (full pdf), providing a check on air travel’s contributions to spreading COVID.

First the update!

We can see that through August (last month of data available as of today), flights are still gradually rising toward a return to 2019 levels, but they’ve still got a loooong way to go. Mostly the rise has been led by domestic air travel within Canada. We can zoom in, looking at monthly passenger totals for 2020 as a percentage of passenger totals for 2019.

Sure enough, by the end of August we’re back up to over a quarter of the Domestic air travel from the same month in 2019. International flights still remain far below 2019 levels, with the biggest drop in Transborder trips between Vancouver and cities in the USA. Miscellaneous International trips that mostly cover Latin America and the Caribbean have seen a recent decline from slightly higher numbers in June and July. Passengers to and from Asia Pacific destinations never dropped as much as other international passengers and have bounced back a little, and passengers to Europe appeared to rise through July and August.

So how are we doing containing COVID exposures on these flights? The BC CDC lists exposures by flight number, origin and destination, and affected rows, and as of today includes exposures through September 30, though given lags in reporting it’s possible the September listings aren’t yet complete (none have yet been listed for October). Here I separate inbound and outbound flight exposures for Vancouver by Origin/Destination Stream roughly matching YVR categories (I remain less certain exactly how flights to and from Mexico fit in, and have included them here as Misc. Intl).

Overall, it’s clear that COVID exposures on flights have declined and then risen again with flights overall between March and August, with the pattern likely continuing into September (again, we don’t yet know if September data is complete and we don’t have YVR passenger data for September yet). Domestic exposures dominate flight exposures overall, especially the rise in August and September.

Finally, we can combine the two sources of data to provide a rough estimate of the inbound and outbound specific risks associated with exposures. How many exposures do we see per 100,000 passengers for different streams of travel? Here I’ve given outbound exposures negative values, and inbound exposures positive values, which tells us something about the direction COVID is traveling relative to YVR during exposure events on flights. I’ve proxied September passenger data with August passenger data to match with September exposure data, and I’ve dropped International Miscellaneous flights, which mostly involve flights to and from Mexico and harder for me to confidently link to passenger data.

A few takeaways:

  1. We get the sense that risks of exposures per 100,000 boardings are real, but generally pretty low, at least as discovered and reported by the BC CDC (where are there have been occasional transparency issues).
  2. We can also see that while most YVR related COVID exposures are happening on Domestic flights between Vancouver and other Canadian cities, the risks of exposure on these flights tend to be lower than the risks of exposure on inbound international flights.
  3. We get a peek at the gateway pattern by which international exposures tend to arrive at YVR from elsewhere, while YVR has tended, in recent months, to send more exposures to the rest of Canada than it receives from Domestic flights.
  4. Finally, while all inbound international travel remains risky relative to domestic travel, European and Transborder (USA) flights generally alternate the lead for most risk, with Asia Pacific flights trailing. That said scanning the international exposure data reveals that European and Transborder risks are generally diverse across cities, while most recent Asia Pacific exposures seem to relate specifically to flights to and from Delhi.

Big takeaway: the tentative and on-going return of air travel will likely continue to contribute to the on-going return of COVID infections, both Domestic and International. Air travel provides a key link between the rise in cases elsewhere and what happens here, potentially turning visitors into vectors. Definitely something to keep an eye on as we continue into Fall!