The 'grey zone' hindering efforts to count Canada's COVID-19 deaths

Along with a drop in the seven-day average of new COVID-19 cases, Canadians have also been seeing a decline in virus-related deaths. From the end of January to the end of February, the weekly average of deaths linked to COVID-19 dropped to 0.16 from 0.44 per 100,000 people. Recent statistics, however, are showing a steady increase in the weekly average of COVID-19-related deaths logged in Canada. As of Feb. 28, the rate is 0.21 per 100,000 people.

Being able to tell the difference between whether a person has died from COVID-19 or a separate cause while infected with the virus is important in understanding the overall trajectory of the pandemic, said Omar Khan, a professor of biomedical engineering and immunology at the University of Toronto. The key lies in identifying the impact of underlying conditions on overall health, he said.

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“We need to understand the differences to know that we are not relapsing into a point where COVID is driving deaths rather than…something else that's making you sick and dying,” he told CTVNews.ca on Feb. 23 in a phone interview. “We need to understand if COVID is continuing to be deadly, or if we've gotten past that point.”

The reality of teasing out this difference, however, is easier said than done, said Matthew Miller, an associate professor at McMaster University’s Michael G. DeGroote Institute for Infectious Disease Research based in Hamilton, Ont. Most patients who die with COVID-19 have underlying medical conditions, said Miller.

Dr. Darren Markland, an intensive care physician at the Royal Alexandra Hospital in Edmonton, said he has been encountering more cases of COVID-19 in people with pre-existing health conditions.

“We're seeing a lot of people who are coming in who have COVID that has exacerbated underlying diseases,” he told CTVNews.ca in a phone interview on Feb. 16. “COVID lowers the threshold for people with underlying problems to get sick enough to come into hospitals.”

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Underlying health conditions, such as high blood pressure, obesity and diabetes, can increase a person’s chances of developing severe COVID-19 illness, said Dr. David Kelvin, a professor in Dalhousie University’s department of microbiology and immunology in Halifax. These conditions can also make it difficult to ascribe a cause of death if a patient passes away, he said.

“It's a very difficult task to sort out what's directly related to COVID-19,” Kelvin said in a phone interview on Feb. 16. “You really need the details on each individual case to assess whether it's directly related to COVID-19 or associated with COVID-19.”

The World Health Organization defines death due to COVID-19 as a death that results from a “clinically compatible illness, in a probable or confirmed COVID-19 case, unless there is a clear alternative cause of death that cannot be related to COVID disease.” International guidelines for reporting COVID-19 as a cause of death require the virus to have caused or be assumed to have contributed to death.

Deaths due to COVID-19, according to the Public Health Agency of Canada (PHAC), are those for which the virus is the underlying cause of death, or the disease that initiated the series of events leading directly to a person’s death. For pre-existing conditions that are believed to increase a person’s risk of severe COVID-19 resulting in death, it should be counted as a death due to COVID-19, PHAC says. However, in situations where death was deemed to be caused by another disease but still influenced by the virus, “COVID-19 should still be recorded on the medical certificates of cause of death, but would not be considered a death due to COVID-19,” reads PHAC’s website.

From a hospital resources perspective, the distinction between dying of COVID-19 and dying with the virus doesn’t matter, said Markland. But when other illnesses are involved, it can be difficult to attribute a primary cause of death when filling out death certificates, he said.

Markland used the example of someone who experiences a heart attack and dies. Typically, the cause of death would be coronary arterial disease, which brought about the attack. With COVID-19, however, studies have shown that the virus damages heart tissue and blood vessels to the heart, said Markland. Patients have often been admitted to hospital with a heart attack who are COVID-19 positive, he said. In this case, depending on when the patient was infected with COVID-19, it’s possible that the virus was the initial cause.

“When you fill in a death certificate, you state the primary cause of death and that is the incident which ultimately leads to someone dying,” he said. “By definition, the thing that initiated the disease process which caused death [in this case] is COVID.”

Ultimately, Markland said, determining the primary cause of death is left to the discretion of the doctor caring for the patient.

“We record who gets COVID and positivity, but it is always left to the physician who's caring for the person at their time of death to make the determination of the cause of death, and that's where the variability comes in,” he said. “You can see how that turns into a very subjective thing.”

Kelvin echoed this, describing situations in which COVID-19 had accelerated a person’s death as a “grey zone.

“It really depends on what your definition is,” he said.

Still, studies show that being vaccinated against COVID-19 greatly reduces the overall risk of hospitalization and death from the virus, even since the emergence of the Omicron variant. A recent study stemming from Ontario demonstrated that two doses of the COVID-19 vaccine decreased the risk of hospital admission and death from Omicron by 82 per cent. A booster dose of the vaccine reduced the risk of severe outcomes by an even greater amount, 95 per cent.

“Vaccines clearly work,” said Kelvin. “The data is spectacular in showing that…fully vaccinated people have a greatly reduced risk of dying and two doses plus a boost enormously reduces your risk of dying from Omicron.”