A study published in The Lancet Global Health reviewed the risk of severe COVID-19 if an individual becomes infected is known to be higher in older individuals and those with underlying health conditions. Understanding the number of individuals at increased risk of severe COVID-19 and how this varies between countries should inform the design of possible strategies to shield or vaccinate those at highest risk.
Andrew Clark, the study’s first author from the London School of Hygiene and Tropical Medicine, said they estimated that 1.7 billion people, comprising 22% of the global population, have at least one underlying condition that puts them at increased risk of severe COVID-19 if infected (ranging from <5% of those younger than 20 years to >66% of those aged 70 years or older). They estimated that 349 million people (4% of the global population) are at high risk of severe COVID-19 and would require hospital admission if infected (ranging from <1% of those younger than 20 years to approximately 20% of those aged 70 years or older). They estimated 6% (3–12) of males to be at high risk compared with 3% of females.
Individuals at increased risk of severe disease were defined as those with at least one condition listed as “at increased risk of severe COVID-19” in current guidelines by age (5-year age groups), sex and country for 188 countries using prevalence data from the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2017 and UN population estimates for 2020. The list of underlying conditions relevant to COVID-19 was determined by mapping the conditions listed in GBD 2017 to those listed in guidelines published by World Health Organization (WHO) and public health agencies in the UK and the USA.
Based on current guidelines, they estimate that about one in five individuals worldwide has an underlying condition that could put them at increased risk of severe COVID-19 if infected, ranging from less than 5% of those younger than 20 years to more than 66% of those aged 70 years or older. However, for many of these individuals, their condition might not be diagnosed or known to the health system, or their increased risk could be quite modest.
They estimate that fewer individuals (about one in 20) would actually require hospital admission if infected, ranging from less than 1% of those younger than 20 years to nearly 20% of people aged 70 years or older, rising to more than 25% in males. Whether or not these individuals are actually infected, and whether or not they receive hospital care if their infection is severe, is beyond the scope of this analysis.
Recent estimates from the UN Economic Commission for Africa suggest that an unmitigated pandemic could lead to a substantial proportion of the African continent being infected and 23 million severe cases of COVID-19 requiring hospitalization.
Their estimates for Africa, based on the same IHRs estimated for mainland China by Verity and colleagues, were higher (42 million vs 23 million), reflecting important adjustments for underlying conditions and age-based frailty. However, even after these adjustments, the total share of the population at high risk is still lower in Africa than in Europe (3·1% vs 6·5%). This evidence will need to be carefully communicated to policy makers to avoid complacency about the risk in Africa.
First, the lower share of the population at risk simply reflects the much younger populations of countries in Africa compared with Europe, and therefore masks the fact that age-specific risks in African countries tend to be similar or higher than age-specific risks in European countries. Second, a much higher proportion of severe cases are likely to be fatal in Africa than in Europe, and disruption to health systems could lead to substantial mortality from non-COVID-19 diseases.
If a safe and effective vaccine is produced, then our estimates provide an indication of the volumes that would be required for vaccination of at-risk individuals globally. In the absence of a vaccine, at-risk individuals might need to be shielded by more intensive physical distancing measures than individuals in the wider population. This approach could be especially important at times and places where health systems risk being overwhelmed by cases. At a minimum, timely information should be provided to communities about who is at increased risk according to current guidelines. Simple tools or classifications could also be developed to help individuals to understand their degree of risk on the basis of their individual characteristics.
Improved population-based screening for high-risk conditions could also be considered. Among those who are identified, governments will rely heavily on their adherence to guidelines, such as increased hygiene, physical isolation, and use of home-delivered food and medical care.
Other infection control measures include provision of personal protective equipment and intensive testing of healthcare and social care workers in maximum contact with at-risk individuals. Incentives could be introduced to encourage at-risk individuals to reduce or abstain from exposure at workplaces or relocate to dedicated safe zones. There is also growing evidence in support of face masks as a means to prevent transmission by those wearing them. If proven to be effective, or if other measures emerge, this could also be a practical way of reducing exposure among those who are unable to avoid contact with others, such as daily wage earners or people living with (or caring for) less vulnerable individuals.
The WHO, along with public health agencies in countries such as the UK and the USA, have issued guidelines on who is considered to be at increased risk of severe COVID-19. This includes individuals with cardiovascular disease, chronic kidney disease, diabetes, chronic respiratory disease and a range of other chronic conditions. Such conditions increase the risk of needing hospital-based treatment such as oxygen supplementation. A large proportion of the additional healthcare burden of COVID-19 epidemics is likely to result from infection of those with underlying conditions.
As the COVID-19 pandemic evolves, countries are considering policies to protect those at increased risk of severe disease. This can involve policies to suppress transmission in the wider population, vaccination (if a vaccine becomes available), or so-called shielding—i.e., specific measures to protect those at increased risk by minimizing interactions between individuals at increased risk and others. Guidelines on who is currently believed to be at increased risk of severe COVID-19 have been published online by the WHO and public health agencies in the UK and the USA.
They searched PubMed using the terms “risk factors” AND “COVID-19” without language restrictions, from database inception until April 5, 2020, and identified 62 studies published between Feb 15 and March 20, 2020. Evidence from China, Europe, and the USA indicates that older individuals, males, and those with underlying conditions such as cardiovascular disease and diabetes are at increased risk of severe COVID-19 and death. At the time of the search, none of the studies identified aimed to quantify the number of individuals at increased risk due to underlying health conditions.
