COVID-19: Age isn’t the only risk factor

At the start of the COVID-19 epidemic, the public health authorities, in Québec and elsewhere, emphasized age as a risk factor. People age 70 and over were identified as most likely to suffer major complications, be hospitalized in intensive care, and eventually die… But age isn’t the only risk factor.

At the start of the COVID-19 epidemic, the public health authorities, in Québec and elsewhere, emphasized age as a risk factor. People age 70 and over were identified as most likely to suffer major complications, be hospitalized in intensive care, and eventually die… But age isn’t the only risk factor.  

People age 70 and over account for 33% of detected COVID-19 cases, even though they are only 13% of the Québec population. But younger people more often are asymptomatic and aren’t detected by screening. Seniors in long-term care centres are tested much more than the rest of the population. So it’s likely that their relative weight among COVID-19 cases is overestimated.  

People age 70 and over account for 72% of hospitalizations (5 times more than their demographic weight). They also account for 92% of deaths (7 times their demographic weight) according to the data of the Institut national de santé publique du Québec. At first glance, age seems to be an important factor. 



But in epidemiology it’s not enough to identify vulnerable groups. You have to try to find out why they’re vulnerable.


What are the risk factors linked to complications and deaths? 

Some COVID-19 victims die quickly, without a known reason. But the vast majority of people who died or were taken to intensive care went through severe respiratory distress. Many already suffered from chronic obstructive pulmonary disease (COPD). It’s known that an excessive inflammatory response, often triggered by COVID-19, mainly attacks the pulmonary alveoli.

The victims also include people suffering from cardiac problems and strokes. Once again, an excessive ventilator response triggers vascular occlusions (thromboses). This happens in 20% to 55% of the cases (and even up to 70%, according to Michelle Sholzberg, a hematologist at St. Michael’s hospital in Toronto. Untreated high blood pressure also leads to this kind of complication. 

Another risk factor is found in diabetes and chronic kidney disorders. They darken the prognosis of the disease, another likely consequence of microthromboses.



Finally, people whose immune system is compromised are also more vulnerable. This is due to a disease like AIDS, or a treatment for an auto-immune disease or chemotherapy.  

Obesity is often mentioned, because it causes a chronic inflammatory condition. It also favours the appearance of heart and circulatory disorders, as well as diabetes.  



A much greater proportion of seniors suffer from these chronic pathologies. 

People over 65 often accumulate more than one of these comorbidities.  

Do these factors explain the complications and deaths? 

According to a compilation by the New England Journal of Medicine, people suffering from these comorbidities account for 38% of the identified COVID-19 cases. But they also account for 71% of hospitalizations, 78% of intensive care patients and 94% of deaths.  

more recent American study published in the Journal of the American Medical Association (JAMA) presents an even higher figure. It covers 5700 patients whose median age was 63, all hospitalized in New York for COVID-19. 6% of the hospitalized patients had one chronic health problem, and 88% had two or more. Only 6% didn’t suffer from comorbidities. This was true for all patients, no matter what their age.  



If these American numbers are confirmed, the presence of preexisting chronic diseases would be a more important hospitalization risk indicator than an age over 70.  

An analogous compilation was produced in Italy by the Instituto Superiore di Sanità, covering 2003 patients who died of COVID-19. It found that 48.5% suffered from three chronic pathologies, 25.6% had two and 25.1% had only one. In fact, only 3 patients out of 2003 died without a preexisting condition (0.7%). The Italian research was conducted at the worst point of the crisis. Several thousand people, still in intensive care, may have died afterwards. It’s likely that the people who initially were in the worst shape died faster. There might be slightly more victims without known comorbidities when the final death toll is published after the pandemic.  


Aging and weakening of the immune system  

Nevertheless, some researchers believe that immunosenescence could contribute to increasing susceptibility to the coronavirus, even if comorbidities are absent. Immunosenescence is the gradual loss of immune system efficiency with age.  This degeneration largely explains why the elderly are so vulnerable to many infections and epidemics, particularly the flu.  

Dr. Richard Marchand, a microbiologist-infectiologist, explained this to columnist Patrick Lagacé in La Presse. Immunosenescence means the COVID-19 virus can reproduce in greater quantities in older patients. They then carry an enormous viral load, making them very contagious. This high contagion index partly explains the quick spread of the virus in long-term care facilities and among caregiving staff.  

Not all seniors suffer from immunosenescence, especially if all people age 70 and over are combined. Age isn’t the only cause. It can also be induced by various chronic viral infections (such as herpes), malnutrition, obesity, alcoholism or smoking. Maintaining a high level of physical activity delays its progression by several years.  

A weakened immune system causes seniors to develop chronic inflammatory diseases. But paradoxically, it may be an advantage against some microbes that trigger an immune system overreaction. This phenomenon is sometimes called a “cytokine storm”. For example, elderly people had fewer complications from the H1N1virus. But the main complications of COVID-19 are associated with such an excessive inflammatory response.  


In conclusion, COVID-19 affects seniors more. Some chronic inflammatory diseases and immune system weakening disease largely seem to explain this situation. This is especially true for older people in poor physical shape.  

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