NEWS

Here’s How Many Vancouver Islanders Might Truly Have COVID-19

By some estimates, up to 100,000 BCers could be hidden survivors of COVID-19

By Tristin Hopper & Harley Gordon

filed from Victoria · Friday, April 17, 2020 · 4 min · a Lochside dog-walk

Crowds in the Inner Harbour during Deuce Days in July, 2019 (Anne Catherine for The Capital).

As of April 17, BC has 1,618 confirmed cases of COVID-19, including 94 on Vancouver Island. But of course, that’s only a small fraction of the total. The singular trait that has allowed COVID-19 to take over the world is that most of the people it infects never show symptoms. On top of that, even among those showing symptoms, BC is only testing select demographics for the virus.

Below, The Capital has used the best available data to prepare several estimates of just how many of us have contracted COVID-19 thus far. These are all extremely back-of-the-envelope calculations, but they help to illustrate why we’ve needed to take such extraordinary measures to tame this disease. The precise numbers below are almost certainly inaccurate, but the fact remains that COVID-19 has spread into our homes and communities far more than we’ll ever know.

Note: The graphs below are interactive. However your cursor over the lines to show relevant labels.

Confirmed cases vs. estimated total cases of COVID-19 using fatality rate estimates

Created with Raphaël 2.1.2

5,000

10,000

15,000

1,517

Actual confirmed cases

16,856

Estimated total cases

Very rough estimates, see notes inline.

One of the most accurate metrics we have for COVID-19 is fatality rate, which currently stands at 78 for British Columbia. Early data out of China showed that approximately 0.66% of total COVID-19 cases were dying. More recently, German researchers testing an entire town for COVID-19 have arrived at a fatality rate of about 0.37%. The chart above, by The Capital data researcher Harley Gordon, splits the difference, assumes a fatality rate of 0.5%, and then calculates the total case rate from that, taking into account incubation periods. It takes about seven days for COVID-19 to kill after the onset of symptoms, so from there you can estimate what the provincial and national case rate would have been a week before a death is recorded.

Estimates for actual BC COVID-19 cases assuming testing catchment of 6% and 9%

28-Jan29-Jan30-Jan31-Jan01-Feb02-Feb03-Feb04-Feb06-Feb07-Feb08-Feb09-Feb10-Feb11-Feb12-Feb13-Feb14-Feb20-Feb24-Feb29-Feb03-Mar04-Mar05-Mar07-Mar09-Mar10-Mar11-Mar12-Mar13-Mar14-Mar15-Mar16-Mar17-Mar18-Mar19-Mar20-Mar21-Mar22-Mar23-Mar24-Mar25-Mar26-Mar27-Mar28-Mar29-Mar30-Mar31-Mar01-Apr02-Apr03-Apr04-Apr05-Apr06-Apr07-Apr08-Apr09-Apr10-Apr11-Apr12-Apr13-Apr14-Apr05,00010,00015,00020,00025,000

Actual confirmed cases

Estimated total cases at 6% testing catchment

Estimated total cases at 9% testing catchment

Estimated total cases at 6% testing catchment

Actual confirmed cases

Estimated total cases at 9% testing catchment

Actual case numbers from the BC Centre for Disease Control

A pair of researchers at the University of Göttingen similarly used mortality rates to estimate that the 40 countries most affected by COVID-19 were likely only catching between 6% and 9% of all cases. There are a whole lot of variables that could make the number of confirmed cases much higher for BC; we’ve had one of the world’s most aggressive testing regimes, and our extremely low death rate points to a much lower prevalence of cases than harder hit areas in New York, Italy or Quebec. However, even at the high end of 9%, we’re looking at 17,000 infected.

Estimates for actual Vancouver Island COVID-19 cases assuming testing catchment of 6% and 9%

Actual confirmed Vancouver Island cases

Estimated total cases at 6% testing catchment

Estimated total cases at 9% testing catchment

Estimated total cases at 6% testing catchment

Actual confirmed Vancouver Island cases

Estimated total cases at 9% testing catchment

Confirmed case numbers from the BC Centre for Disease Control

And these are the estimated totals for Vancouver Island using the University of Göttingen numbers, showing that as many as 1,500 Islanders might be hidden or untested COVID-19 cases.

Estimated actual COVID-19 cases for BC, assuming 50 and 85-fold totals of test-confirmed cases

Actual confirmed BC cases

Total cases at 50-fold estimate

Total cases at 85-fold estimate

Total cases at 50-fold estimate

Actual confirmed BC cases

Total cases at 85-fold estimate

In a just-published study, Stanford University researchers took a representative sample of the population of Santa Clara County, California and tested everyone in that sample for evidence of antibodies related to COVID-19. The study was intended not just to show who currently had COVID-19, but who might have already contracted it and fought it off without knowing. The study’s very surprising result was that for every known case of COVID-19 in Santa Clara County, there were likely between 50 and 85 unknown cases. The chart above takes BC’s known case numbers, and simply multiplies them by 50 and 85, respectively.

Estimated actual COVID-19 cases for Vancouver Island, assuming 50 and 85-fold totals of test-confirmed cases

Actual Island cases

Total cases at 50-fold estimate

Total cases at 85-fold estimate

Total cases at 50-fold estimate

Actual Island cases

Total cases at 85-fold estimate