Elderly Canadians remain at higher risk of serious COVID from first infections, study suggests

New Canadian data reaffirms that while the vast majority of the population has likely caught the virus behind COVID-19 at least once, more than four in 10 elderly adults may have avoided infection so far — while remaining at the highest risk for hospitalization and death.

It's yet another reminder that seniors need to be prioritized in vaccination rollouts and should strongly consider getting an updated COVID shot, several medical experts told CBC News.

The latest findings come from a study conducted in British Columbia's Lower Mainland and published on Monday in the Canadian Medical Association Journal.

The researchers looked at both seroprevalence — signs of prior SARS-CoV-2 infection in blood samples from various age groups, at different points in the pandemic — and health-care data on severe illness.

The team found that by July, more than 80 per cent of children and adults under 50 had been infected and had a low risk of hospital admission or death.

But for seniors aged 80 and older, more than 40 per cent had never been infected by the virus, their data showed. That age group also had the highest risk of serious outcomes.

"First infections among older adults may still contribute substantial burden from COVID-19," the authors wrote.

Lead investigator Dr. Danuta Skowronski, a researcher and epidemiologist with the B.C. Centre for Disease Control, said the latest findings are the culmination of years of work done throughout the pandemic, including 10 rounds of seroprevalence surveys.

Her team's most recent round of research estimated one death for every 80 newly infected seniors who are 80 and older.

Among all age groups, she said, there has been a decrease in severe outcome risks over the course of the pandemic, including among seniors.

"But for the older segment of the population," Skowronski said, "it's still a meaningful risk."

Vaccines particularly crucial for seniors

Federal data shows seniors have long borne the brunt of the COVID pandemic, facing far higher death tolls than younger age groups — including devastation within long-term care homes housing the country's frail and elderly.

And while a growing body of evidence suggests that people with a history of both vaccination and prior SARS-CoV-2 infection are at lower risk of severe outcomes — when compared with those with neither, or just a prior exposure alone — experts say the takeaway is not for seniors to now throw caution to the wind.

"Certainly, we wouldn't encourage people to deliberately get infected," Skowronski said.

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"What we're saying is that for those who have been infected, in combination with vaccination, they are better protected. Rather, our emphasis is — because we observed that the oldest of our population remain at highest risk of severe outcomes — that they should continue to be prioritized for vaccination."

Several medical experts agreed that vaccination campaigns need to stress that seniors should strongly consider getting this fall's updated COVID shots, which have been tailored to better match the virus strains currently circulating.

"I'm not sure if that message has been coming through clearly enough," Skowronski said.

Dr. Zain Chagla, an infectious diseases specialist at McMaster University in Hamilton, said the study shows that for older Canadians, particularly those 80 and up, the outcome of their first infection still remains unclear.

Focused campaigns targeting seniors to encourage vaccination uptake are crucial, he said.

"There is a real recognition here that age is probably the simplest and easiest thing to target," Chagla said. "And it's one that probably needs to be front of line in most of these campaigns moving forward."

Findings may show 'worst-case scenario'

The B.C. research relied on blood samples taken from various individuals over the last few years, not specifically to study COVID but for myriad other health-related reasons — giving Skowronski's research team ongoing snapshots of immune activity throughout the population.

Speaking to CBC News from her office in the greater Montreal area, family physician Dr. Laura Sang said she was impressed with the quality of the latest paper. "It seems like a really robust and rigorously done cross-sectional study," she said, adding: "The findings are not surprising."

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But Chagla said the study's approach may have been hindered by waning antibodies in people's blood, leading to an underestimate of the true number of prior infections. The research team also didn't test and retest the same cohort of people over time but rather looked at fresh sets of 2,000 anonymous blood samples.

Skowronski's team was aware of those limitations but said that on the flip side, the risks of hospital admission or death could actually be overestimated.

"Even though our estimates of the risk of severe outcomes were low, they are likely even lower for most of the population, particularly among those both previously vaccinated and infected who are now the majority," the researchers wrote.

In other words, Skowronski said, her team's findings might be showing the "worst-case scenario."

'Socialize smartly,' take basic precautions

Sang agreed that an underestimation of seroprevalence would actually be "good news."

"That means lower risk for everyone," she said. "But it's still worth erring on the side of caution."

For all higher-risk individuals, including seniors — and particularly those who haven't yet experienced their first confirmed SARS-CoV-2 infection — Sang recommended maintaining basic precautions throughout the fall and winter.

Those measures include getting a COVID vaccine, practising basic hand hygiene, wearing a mask in public and disinfecting high-touch surfaces, Sang said. She also encouraged seniors to "socialize smartly," in smaller groups and in well-ventilated areas, or even outside when possible.

For seniors who think they have COVID, she said it's worth taking a rapid test and contacting your primary care provider to find out if you're eligible for treatments like Paxlovid.

It's also important to continue managing any other underlying health conditions, such as diabetes, high blood pressure or chronic obstructive pulmonary disease (COPD), to reduce your risk of severe illness from COVID.

"And if you feel that things are progressing or going in the wrong direction, promptly seek care," Sang said.