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After the first wave of the Covid-19 pandemic brought a surge in death rates, the second wave was less intense but lasted longer, according to new data from Statistics Canada.

StatsCan reported that Canada recorded an estimated 18,511 excess deaths from the start of the pandemic in March 2020 through to March 2021, representing 6.7% more deaths than expected in that period.

This higher-than-expected death count was concentrated in two distinct waves — March to June 2020, which saw 8,423 excess deaths; and September 2020 to early February 2021, when there were 9,117 additional deaths.

“While this second period of excess mortality was almost twice the length of the first period (in the spring of 2020), the average number of excess deaths per week was lower,” StatsCan noted, adding that the peak was also less pronounced in the second wave.

Additionally, the agency reported that, while excess death numbers closely tracked Covid-19 death counts during the first wave, these trends have diverged over time.

“A closer examination of the patterns for different age groups reveals a growing disconnect between the population groups experiencing excess mortality and those most affected by Covid-19 deaths,” it said.

For instance, among those aged 84 and up, there were 4,197 excess deaths during the first wave and 4,725 deaths caused by Covid-19. In the second wave, there were 3,691 excess deaths among the age group and 5,420 deaths attributed to Covid-19.

“The higher number of Covid-19 deaths may be attributable to the disease taking a heavy toll on some individuals who may have been at a high risk of dying over this period of time, regardless of the pandemic. In addition, the indirect effects of the pandemic, possibly resulting in decreases in the number of deaths attributable to other causes, could also be at play,” StatsCan said.

A similar trend was observed in the 65 to 84 age group, whereas for those younger than age 65 the number of excess deaths is higher than the number of deaths attributable to Covid-19, StatsCan reported.

For example, the 45 to 64 age group accounted for just 6% of Covid-19 deaths but made up 16% of overall excess deaths between March 2020 and March 2021.

The under-45 age group has also experienced “significant excess mortality” despite accounting for less than 1% of Covid-19 deaths, the report said.

Many of these added deaths are likely due to indirect effects of the pandemic, such as mental health impacts and drug abuse.

“Some provincial authorities, such as in Alberta, have reported that more deaths were attributed to overdoses in 2020 than in any previous year,” StatsCan said.

The agency said its provisional data suggests that Covid-19 was the third most common cause of death in 2020, accounting for about 5% of all deaths.

Cancer remained the top cause at 26%, followed by heart disease (17%).

Among those younger than 65, Covid-19 accounted for about 2% of deaths, well behind cancer (35%), heart disease (14%) and accidents (5%), which includes overdoses, traffic fatalities and other unintentional injuries.

For those under 45, accidents is the top cause (19%), followed by cancer and suicide (10% each).