When the COVID-19 pandemic began to spread and kill hundreds of thousands globally in 2020, governments’ priority was to reduce hospitalisations and intensive care unit (ICU) admissions to avoid overwhelming health systems.
While Asian countries could rely on their high testing capacity and great willingness to monitor and enforce compliance, Europe and the USA were obliged to rely more heavily on general measures, such as physical distancing, mask-wearing, hand hygiene and lockdowns, which are designed to reduce transmission in the population as a whole.
But specific subgroups of the population, such as the elderly and the frail, were deemed to contribute disproportionately to adverse outcomes and healthcare demand. In some countries, such as Scotland and Sweden, people at high risk of severe COVID-19 disease were asked to shield themselves during the first wave of the pandemic while a lower level of restrictions was imposed on younger groups.
“Until April last year, there was a view that COVID-19 was just a problem in the elderly,” says Professor Bruce Thompson, dean of the School of Health Sciences at Swinburne University of Technology, Melbourne.
A new study published today in Scientific Reports found that simply isolating people is not enough to shield our most vulnerable from COVID-19. Other population-wide measures must be implemented simultaneously, such as social distancing, face masks, and hand hygiene.
Researchers from the University of Glasgow analysed data from 1.3 million patients around Glasgow, Scotland, between March and May 2020. Of these, over 27,000 were considered high-risk and told to self-isolate for extended periods. The rest of the patients were not asked to self-isolate. Amongst these, the authors extracted over 350,000 individuals who were considered at medium risk of COVID-19 due to health conditions and comorbidities. The more than 930,000 remaining patients were considered low risk.
The team found that high-risk people who had been advised to self-isolate were eight times more likely to contract the COVID-19 infection and five times more likely to die than low-risk individuals. Moderate-risk individuals were four times more likely to catch COVID-19 and five times more likely to die than those in the low-risk group.
“Our findings suggest that attempts to shield those at highest risk have not been as successful as hoped,” wrote the authors.
The authors suggested that for shielding to be effective as a population-level strategy, not only the elderly but also those with comorbidities must be recommended to shield during an outbreak. “In our study, more than one-quarter of the general population would have needed to be effectively shielded to prevent over 80% of deaths,” they wrote.
“Ultimately, there’s a chink in the armour,” says Thompson. “As soon as you bring the virus into something, there is a risk.”
The authors of the study caution that while their findings are representative of the Greater Glasgow and Clyde National Health Service area, they may be less so for other areas or countries with different levels of support, monitoring or compliance.
In Scotland, shielding was recommended but not monitored or enforced. The researchers found that only 40% of people advised to shield stringently followed the recommendation. In comparison, 21% reported they were unable to comply because they had to support other household members, care for pets, avoid domestic abuse, or undertake essential chores. Many also highlighted the difficulty of social distancing within their nursing homes.
“Context is really important,” says Thompson. Different health systems, population density and demographics, and even different climates, can make it challenging to compare Scotland to Australia, he says. But solely asking our elderly to shield while the rest of us go on with our lives, Thompson says, would probably not work here either: “The evidence suggests that population-wide, hard lockdown does work in Australia. But it might not work in Scotland.”
The authors of the study concluded that shielding could probably be best viewed as an intervention to protect individuals. But population-wide interventions such as physical distancing, face coverings and hand hygiene must be maintained.
“The best form of shielding is vaccination,” says Thompson. “As soon as you’re vaccinated, you’ve turned COVID into a different disease. You change its mortality profile hugely.”
That is true even for immunocompromised people at an increased risk of developing severe COVID-19 infection and who are less likely to mount a high immune response through vaccination.
“The vaccination still works,” says Thompson, who takes immunosuppressant drugs due to rheumatoid arthritis. He says he is waiting to receive his second AstraZeneca shot at the end of August and expects to receive a booster in the following months.
“Just because you’re immunocompromised, it doesn’t mean [vaccination] is not effective,” he says. “It may not be as effective as in a person with a robust immune system, but it’s still highly effective in preventing a very severe illness.”
But for quite some time, Thompson says, no one can rely on herd immunity: “We will be socially adapting to wearing masks, hand hygiene, contact tracing, use of QR codes, and surveillance for a while.”
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Dr Manuela Callari is a Sydney-based freelance science writer who specialises in health and medical stories.
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