As the COVID-19 pandemic continues in Alberta, there are so many numbers flying around, it’s hard to keep track.
Here, we’ll do our best to keep track for you.
Below you’ll find a series of curated charts, which will be updated as new information becomes available.
You’ll also find brief descriptions of how the data is measured, what it shows — and what it doesn’t show. This context is important to make sense of the numbers.
We’ll start with new cases.
These are the figures that tend to be front and centre in the daily updates about COVID-19.
There are some issues with relying on new-case data, alone, as the number of cases you detect is related to the amount testing you do and who you’re testing (more on that in a moment).
But the advantage of looking at new cases is that they tend to be a leading indicator of how the virus is spreading, where it’s spreading, and whether the spread is speeding up or slowing down.
This first chart shows us the number of new cases identified each day since mid-March, and a seven-day average of daily new cases.
A common question about these case numbers is why they don’t always match the numbers cited by Alberta’s chief medical officer of health, Dr. Deena Hinshaw, when she gives her public updates.
That’s because Alberta Health actually reports two sets of case numbers: a simplified net count and a regularly updated detailed count.
These two counts can vary slightly on some days because there is always a little uncertainty in the latest daily numbers.
Sometimes Alberta Health learns, days after counting a “probable” case of COVID-19, that it actually wasn’t a true case of the disease. In that event, the case is subtracted from the count. Other times, new information comes in late about a case that wasn’t initially included in a day’s tally. In that event, the case is added to that day’s count.
These fluctuations mean that Alberta Health is constantly adjusting its data, and it does so in two ways.
In the simplified numbers (which Dr. Hinshaw cites and are also posted on this section of the Alberta Health website), these fluctuations are netted out, so that the numbers reported each day add up to the total number of cases.
In the detailed data (which are posted on this other section of the Alberta Health website), the case counts are retroactively adjusted as new information comes in.
The data in the charts presented here come from the detailed data, not the simplified numbers, and thus are retroactively updated in the same way.
Vaccinations continue to roll out to more and more Albertans, but the pace of immunization has ebbed and flowed along with the supply of vaccine arriving from manufacturers to the federal government, which then distributes them to Alberta.
This next chart shows vaccination progress in terms of the total number of doses distributed to Alberta (the dotted line) and the total number of shots administered to Albertans (the solid line).
Health-care workers and residents of long-term care homes were among the first to receive the vaccines in Alberta, and many were given the full two doses on (or near) the manufacturers’ originally recommended schedules.
But as time went on, Alberta and other jurisdictions (both in Canada and around the world) changed strategy and opted to give single doses to more people as soon as possible, deferring the second doses until later on.
This next chart shows the percentage of Albertans who have been fully immunized (the green line) and the percentage who have received at least one dose of vaccine (the blue line).
For more information on how Alberta’s vaccine distribution compares to other provinces and territories, check out CBC’s national vaccine tracker.
In early 2021, Alberta Health started reporting more data on new variants of the virus that causes COVID-19.
Two variants of particular concern are known as B117 (which originated in the United Kingdom) and B1351 (which originated in South Africa.) A variant known as P1 (which originated in Brazil) was later added to this list.
These variants have numerous genetic mutations compared with the dominant type of virus that circulated in Alberta in 2020. They are of concern to public health officials because they are believed to transmit more easily from person to person.
The first case of B117 in Alberta was reported on Dec. 28, although it was actually detected earlier in December in a retrospective analysis of a sample that had been taken from a COVID-positive patient.
The following chart shows total cases of each variant, by the date they were reported to Alberta Health. This is typically the date that a specimen was found to be positive for COVID-19, not necessarily the date the swab was taken from a patient’s nose or throat.
It takes additional time for a COVID-positive specimen to then be screened for variants of concern, so the data for the most recent few days are usually an undercount.
By February, Alberta Health was testing all positive specimens for variants of concern. Prior to that, it was selectively testing specimens retrospectively, focusing on returning travellers who had tested positive for COVID-19.
By March, it had become clear that one variant in particular had become more established in Alberta: B117.
This next chart shows the growth in that variant, specifically.
The most recent two days’ worth of data are excluded from the above chart, due to the lag in variant screening, which leads to those days being a particularly large undercount.
Alberta Health also breaks down where the variants have been detected, by health zone.
You can see the latest breakdown in this next table.
Of course, Alberta is a big province and it’s not just the new variants that have seen geographic variation.
At different times throughout the pandemic, different parts of the province have seen different degrees of virus spread.
So it’s useful to look at where new cases, in general, have happened, too.
New cases by health zone
Alberta Health breaks the province down into five broad health zones: South, Calgary, Central, Edmonton and North. (The names are pretty self-explanatory but if you want to see the precise boundaries of each zones, here’s a link to a PDF map.)
This next chart shows new cases, by day, broken down by health zone.
Each column in this chart is a “stack” of cases, colour-coded by zone. Each “stack” adds up to the total number of new cases identified that day.
You can see how cases really started ramping up in mid-April in the Calgary Zone, in particular. This was largely related to the major outbreak at the Cargill slaughterhouse in High River, which is part of the Calgary Zone.
Later in April, you can see a large number of new cases in the South Zone. This was related to the outbreak at the JBS slaughterhouse and the wider outbreak in Brooks at that time.
In early June, you can see how new cases started growing in the Edmonton Zone again, after very few cases in and around the city for many weeks. The beginning of this trend was initially linked to several family gatherings in the city.
And then in October onward you can see the late-year surge in cases, which includes all health zones but has been most heavily concentrated in the Edmonton and Calgary areas.
So that’s the big picture, but the chart above can be a little hard to read if you’re mainly interested in recent cases.
This next chart shows the same information, but is limited to just the past three weeks, making it easier to see where new cases have been popping up. Tap on the bars or scroll your mouse over them to see specific numbers.
Some of these new cases will require hospitalization, which leads us to the next metric.
While much of the COVID-19 reporting focuses on the number of cases, experts are also closely tracking the number of hospitalizations.
Hospitalization data is more of a lagging indicator, as it typically takes longer for someone who gets sick with COVID-19 to end up in hospital than it does for them to test positive for the virus. There can also be delays in reporting from the hospitals, themselves, further adding to the lag in the aggregated data.
Still, tracking hospitalizations is useful because it not only helps gauge how much the disease has spread but also helps keep track of how much strain is being put on the health-care system. Hospital resources, of course, are finite and, in other parts of the world, COVID-19 cases have pushed those resources to — or beyond — their capacity.
Prior to November, hospitalizations had not reached a level anywhere near the capacity of Alberta’s critical-care system.
But we can’t tell you exactly what that capacity is — or how close were are to it — because the capacity can change and total ICU occupancy data isn’t available publicly.
While Alberta Health provides regular updates on the number of COVID-19 patients in intensive care, Alberta Health Services (AHS) won’t release similar data on the total number of patients in ICU. As a result, we can’t say exactly how many ICU beds are available at a given time.
CBC News has repeatedly asked for this data but AHS has not been willing to provide it.
AHS has said it monitors ICU capacity internally and is able to move patients, staff or equipment to match the need. It is also able to expand the overall ICU capacity, if need be, but there would be trade-offs to be made in other areas of the health-care system if that were to happen.
Specialized units — such as those intended for cardiac or neurological patients — can be repurposed for COVID-19 patients, but that means they won’t be available for people suffering from heart or brain conditions.
In an extreme case of ICU demand, non-traditional hospital space such as resuscitation bays in emergency departments and post-operative recovery rooms could converted into intensive care units. But again, that would mean those resources aren’t available for other types of patients.
In November, Hinshaw said the province had about 70 ICU beds set aside for COVID-19 patients and, as the number of patients approached that level, she said additional ICU beds could and would be devoted to people suffering from severe effects of the disease.
To provide some further context, this next chart shows the hospitalization rate in select provinces.
This is a population-adjusted measure, calculated as the number of patients in hospital (of all kinds, not just ICU) per million residents.
Note the numbers in the above chart are collected nationally so the dates are slightly different from the Alberta-specific data.
These numbers are also sometimes retroactively updated to reflect the latest totals, as new hospital data comes in.
Hundreds of Albertans have now died of COVID-19 but the rate of deaths has fluctuated throughout the pandemic.
This next chart shows the number of deaths, by day.
There is often a lag between when a person dies and when it is reported to Alberta Health, so the number of deaths for the most recent few days tends to be under-reported.
The vast majority of deaths have occurred among Albertans over the age of 60, and people over the age of 80 make up more than half of the total deaths, to date.
For a more detailed, age-based breakdown of disease outcomes scroll down to the chart below labelled “COVID-19 cases in Alberta, by age and status.”
Active and recovered cases
Another term you often hear in discussion of COVID-19 is the number of “active” and “recovered” cases.
In general, Alberta Health says a recovered case is defined as:
- Anyone who is healthy after 14 days have passed, if they did not experience severe symptoms requiring hospitalization.
- Anyone who has gone 10 days from their date of discharge from hospital, if they did require hospitalization.
- Anyone who has received two negative tests, at least 24 hours apart.
This next chart depicts the total number of cases, broken down by the status of the patients: recovered, not-yet-recovered (but not in hospital), hospitalized or deceased.
Again, this chart is a “big picture” look at the impact of the disease, provincewide.
But the number of active cases can vary quite a bit from place to place and from time to time.
So this next chart focuses on just the past three weeks, and breaks down the active caseload by health zone.
Beyond these five broad zones, Alberta Health breaks down the geography of the province even further.
It also subdivides those zones in 132 “local geographic areas” or LGAs. (You can find more information about these areas here.)
The right-hand column in the table below shows the latest active caseload for each of those local areas, along with mini-line charts depicting the caseload history for each area since mid-April. (Note the scale of vertical axis is not the same for each line chart; it’s specific to each local area’s case history.)
The table may not display fully on mobile devices or small screens. In that case, you can also click here to open a standalone version in a new browser tab.
The table is sorted from highest to lowest and shows 10 local health areas at a time. You can click on the next-page arrows to see more, or use the search function to look for a particular area.
You can also see active cases by local health area on the following interactive map. Scroll, zoom and click on the map for more information.
The map shows both the active case numbers (labels that appear when you zoom in) and the active-case rates per population (the background shading.)
If the map isn’t displaying well on your mobile device, click here for a standalone version.
And you might also be wondering how Alberta’s active caseload compares to the rest of the country. This next chart illustrates that.
The chart shows the rate of active cases (number of cases per 100,000 population) in each province and territory and in Canada, as a whole.
You can click or tap on the buttons above the chart to switch between the per-capita rate and the absolute number of active cases in each province and territory.
Total confirmed cases
The term “flatten the curve” has become a common phrase used by people when referring to stopping the spread of the COVID-19.
One “curve” that people have been paying attention to, especially early in the pandemic, is the total number of cases.
Early in the outbreak, the number of cases was growing rapidly, with the total doubling every three days.
Later on, that rate of growth started to slow, and the curve “flattened” — to a degree. The outbreaks at the slaughterhouses in High River and Brooks, in particular, shot it back up again, as did smaller, localized outbreaks in other areas. Case growth slowed in the summer then started to accelerate again in late September.
The red line in this next chart shows the cumulative total of COVID-19 cases in Alberta.
The background shading shows various stages of the province’s public-health measures, from the initial pandemic response (colloquially referred to as the “lockdown”) to Stage 1 and Stage 2 of the “re-launch” strategy.
When looking at total cases, it’s important to bear in mind that the number of confirmed cases doesn’t represent the number of actual cases — a figure we simply don’t know.
Many cases may have gone undetected because people didn’t have symptoms or didn’t seek testing for other reasons. People who have wanted a test haven’t always been able to get them, especially early in the outbreak.
Alberta’s testing protocols have changed significantly over time, leading to changes in which cases of COVID-19 are being caught and included in the provincial data — and those which go uncounted.
How testing has changed over time
It the earliest stages of the outbreak, testing focused on international travellers returning to Alberta and their close contacts.
On March 23, the province imposed stricter limits on who could get tested, giving a higher priority to those most at risk from COVID-19 and to health-care workers. Given that testing capacity was limited at that time, there were some important reasons for doing this, in order to get the maximum benefit out of the tests that were available. As testing capacity increased again, however, the criteria began to expand.
On April 7, the province started opening up tests to more symptomatic people, including a wider range of front-line workers such as firefighters, police and public-health inspectors, as well as anyone over the age of 65.
On April 8, the criteria were further expanded to include anyone with symptoms living in the Calgary health zone, which has seen the majority of cases so far in the province.
On April 14, the criteria were expanded again to include all Albertans showing symptoms.
On April 17, Alberta Health said it would further expand testing to include asymptomatic residents and staff in continuing care facilities experiencing outbreaks.
On May 11, asymptomatic testing was extended to people in the Calgary health zone, due to the high number of cases in the area. Similar asymptomatic testing was later offered in Brooks, as well, after the major outbreak in that city.
On May 29, asymptomatic testing was expanded to the entire province, meaning any Albertan wanting a test could seek one, even without symptoms of COVID-19.
On Sept. 17, asymptomatic testing for Albertans with no known exposure was scaled back to include “priority groups” only, such as residents and staff in congregate settings, health-care workers, teachers and other school staff and people experiencing homelessness.
On Oct. 20, Dr. Hinshaw said the province would be “pressing pause on all asymptomatic testing in those who have no known exposure.” At that point, she said Alberta had completed more than 659,000 tests, in total, on asymptomatic people with no known exposure and, of those, only 0.11 per cent came back positive.
All these changes have led to major fluctuations in the number of tests being performed and who was being tested.
It’s important to bear these changes in mind when considering another measure health officials track: the positivity rate. This is simply the percentage of tests that come back positive.
This next chart depicts the positivity rate in Alberta over time.
Each dot depicts the percentage of positive tests on a given day. The line shows the average positivity rate over the previous seven days.
The background shading and annotations show major changes in the testing protocol over time.
Age of patients
The age of Albertans who are diagnosed with COVID-19 has varied over the course of the pandemic.
At different times, the disease was being found more often in younger people, older people or middle-aged people due to a variety of factors.
This next chart shows the case rates in five broad age groups.
Because the number of Albertans in each age group varies widely, the rates are expressed in terms of new daily cases per 100,000 people in a given age range, to account for these population differences.
You’ll notice the case rates among Albertans aged 80+ start to diverge from the other age groups in early 2021, especially in March. At this time, even as case rates rose sharply in the general population, the rate in this age group declined. Alberta Health attributes this difference to the fact that seniors were the first to get widely vaccinated.
We’ve heard that COVID-19 tends to hit older people harder than younger people, and this is true to a large extent but it doesn’t mean young people are immune.
This next chart shows the age ranges of patients who have been hospitalized in Alberta with the disease.
The numbers in this chart are cumulative totals that include patients who are still in hospital, those who have been discharged and those who have died.
The number of people to have died from the disease is much more heavily weighted toward older adults, with most of the deaths among people aged 80 or over. Many of these people have died in long-term care homes.
This last chart shows the total cases in Alberta, broken down by both the age and status of the patients.
The COVID-19 situation continues to evolve rapidly. If you have an idea on how to improve the presentation of these data, or data that you would like to see that’s not here, please email firstname.lastname@example.org. You can also contact Robson on Twitter @CBCFletch and join the discussion there.