Here are the latest COVID-19 statistics for Alberta and what they mean

Update: We updatedand reposted this story almost every day for 582 days during the early daysof the COVID-19 pandemic in Alberta and subsequent waves and want to thank you, our audience, for the enthusiastic feedback over those many months:we're so glad you found ituseful. Wewill no longer be updating itas of Nov. 2, 2021, but you can find all the latest important developments on COVID-19 in Alberta on our CBC Calgary and CBC Edmonton websites.

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.

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 of 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, 2020, and a seven-dayaverage of daily new cases.

A common question about these case numbers is why they don't always match the numbers cited byAlberta'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 simplifiednet 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 latestdaily 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

Vaccinations continue to roll out to more and more Albertans, but the pace of immunization has ebbed and flowed along with the supply of vaccinearriving 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.

Vaccines were then largely rolled out by age, meaning older Albertans had earlier opportunities to be vaccinated.

In this next chart, you can see how the number of people who have received at leastone dose compares with the number of unvaccinated people in each age range.

And finally, it's helpful to look at the proportion of people who have been vaccinated.

This next chart shows the percentage of Albertans, by age, who have received at least one dose of vaccine, two doses, or no vaccination.

In mid-May 2021, Alberta Health also started publishing detailed geographic breakdowns of vaccination rates, by age.

This next interactive shows the percentage of population in each of 132 "local geographic areas" defined by Alberta Health.

You can click or tap on the drop-down menu to select a particular area. They are listed in alphabetical order.

Note that the boundaries of these "local geographic areas" do not necessarily correspond exactly to the boundaries of municipalities with the same or similar names.

To see the exact boundaries of these "local geographic areas,"scroll down to the interactive map in theActive and recovered cases section below.

For more information on how Alberta's vaccine distribution compares to other provinces and territories, check out CBC's national coronavirus tracker.

New variants

In early 2021, Alberta Health started reporting more data on new variants of the virus that causes COVID-19.

Two variants of particular concernare known as alpha or B117 (which originated in the United Kingdom) and Beta or B1351(which originated in South Africa.) A variant known asGamma or P1 (which originated in Brazil) was later added to this list, and after that came the first confirmed cases of the delta or B1617 variant, first identified in India.

These variants have numerous genetic mutations compared with the dominant typeof 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 alpha variant in Alberta was reported on Dec. 28, although it was actually detected earlier in Decemberin a retrospective analysis of a sample that had been taken from a COVID-positive patient.

It takes additional time for a COVID-positive specimento then be screened for variants of concern, and the tests for some variants can take longer than others. So, it's often days later that a confirmed case is identified as a particular variant.

By February, Alberta Health was screening 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.

Not all specimens can be screened, however. Due to limited genetic material or other technical issues, Alberta Health Services said in March that roughly 80 to 85 per cent ofsamples were being successfully screened.

As ofMay 1, 2021, however, Alberta Health hadstopped screening all positive specimens for variants of concern.

The province said the move was necessary in order to maintain turnaround times and capacity in laboratories, which had been falling behind in the wake of the third wave that pushed case counts higher than they had ever been before.

Full screening resumed as of June 1, as case counts dropped and labs were no longer overwhelmed.

Then in September, amid the surging case counts of the fourth wave, labs scaled back their variant screening again.

As a result of these changes, this next chartoffers as complete of a picture as possible of variant spread, but the numbers prior to February, throughout the month of May, and from Sept. 10onward are not directly comparable to the rest.

The chart above shows total cases of each variant, by the date they were reported to Alberta Health, and reported as a seven-day moving average.

It can also be helpful to look at each variant relative to the other variants, to understand which versions of the virus are out-competing the others.

The alpha variant became dominant in Alberta in the spring,but later on the delta variant started to gain more and more of a foothold in the province.

This next chart shows each variant of concern, as a percentage of all new variant cases on a given day.

The original "wild type" of the virus (which contains no major mutations) still circulates in small numbers, Alberta Health said in June 2021, but variants make up the overwhelming majority of cases.

Alberta Health also breaks down where the variants have been detected, by health zone.

You can see the latest breakdown in this next table. Again, the totals will not reflect the total number of actual variant cases, due to the fact that not all samples are being screened.

Of course, Alberta is a big provinceand it's not just the new variants that have seen geographic variation.

At differenttimes throughout the pandemic, different parts of the province have seen different degrees of virus spread.

So it's useful to look at wherenew 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 first started ramping up in mid-April 2020 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 thatmonth, 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 Brooksat that time.

In early June 2020, 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 2020 you can see thelate-year surge in cases, which includedall health zones but was most heavily concentrated in the Edmonton and Calgary areas.

That was followed by the "third wave" in early 2021, which saw the highest daily case counts of the entire pandemic.

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.

Hospitalizations

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 the second wave that hit Alberta in late 2020, hospitalizations had not reached a level anywhere near the capacity of Alberta's critical-care system.

In November 2020, 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 additionalICU beds could and would be devoted to people suffering from severe effects of the disease.

Alberta Health Services 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 repurposedfor COVID-19 patients, but that would mean they won't be available for people suffering from heart or brain conditions.

In May 2021, Alberta Health started publishing data on ICU capacity.

Alberta typically has 173 general, adult ICU beds across all its hospitals but, during the pandemic, that capacity has been expanded. The exact capacity on a given day can vary depending on the availability of trained staff.

This next chart shows the typical capacity, the day-to-day expanded capacity, and the number of COVID-19 patients and total patients in ICU.

ICU occupancy peaked in May 2021 and then started to decline, as more and more Albertans were vaccinated against COVID-19.

This next chart shows the number of patients in ICU, by their vaccination status:

• no vaccination.
• having had a single dose within 14 days of their diagnosis.
• having had a single dose more than 14 days before their diagnosis.
• having had a second dose within 14 days of their diagnosis.
• having had a second more than 14 days before their diagnosis (i.e. being fully vaccinated).

The chart is also annotated to show when one quarter and one half of the total population had received at least one dose, and when half of the population had received two doses.

Deaths

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 scrolldown 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 arecovered 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 areashere.)

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 2020. (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 alsoclick 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 or tap on the map for more detailed information about a particular area.

As you zoom in, the map will display labels showing the actual numberof active cases in each local area.

It also shows the population-adjusted active-case rates(cases per 100,000 people) through the background shading. The darker the shade, the higher the rate.

If the map isn't displaying well on your mobile device, click here for a standalone version.

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.

When talking about COVID-19 cases, it's important to bear in mind that the number of confirmed cases doesn't represent the number ofactualcases 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 also 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, 2020, 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 waslimitedat 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, 2020, the province startedopening 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, 2020, the criteria were further expanded to include anyone with symptoms livingin the Calgary health zone, which hadseen the majority of cases so far in the province.

On April 14, 2020, the criteria were expanded again to include all Albertans showingsymptoms.

On April 17, 2020, Alberta Health said it would further expand testing to include asymptomatic residents and staff in continuing care facilities experiencing outbreaks.

On May 11, 2020, 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, 2020, asymptomatic testing was expanded to the entire province, meaning any Albertan wantinga test could seek one, even without symptoms of COVID-19.

On Sept. 17, 2020, asymptomatic testing for Albertans with no known exposurewas scaled back to include "priority groups" only, such asresidents and staff in congregate settings, health-care workers, teachers and other school staffand people experiencing homelessness.

On Oct. 20, 2020, Dr.Hinshawsaid the province would be "pressing pause on all asymptomatic testing in those who have no known exposure." At that point, she said Alberta hadcompleted more than 659,000 tests, in total, on asymptomatic people with no known exposure and, of those, only0.11 per cent came back positive.

All these changes haveled 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 consideringanother 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 caseratesin 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 chartare 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 robson.fletcher@cbc.ca. You can also contact Robson on Twitter @CBCFletchand join the discussion there.