How many are at increased risk of severe COVID-19 disease? Rapid global, regional and national estimates for 2020

Andrew Clark; Mark Jit; Charlotte Warren-Gash; Bruce Guthrie; Harry HX Wang; Stewart W Mercer; Colin Sanderson; Martin McKee; Christopher Troeger; Kanyin I Ong; Francesco Checchi; Pablo Perel; Sarah Joseph; Hamish P Gibbs; Amitava Banerjee; Rosalind M Eggo

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, a key option to mitigate the pandemic is to shield at-risk individuals by more intensive physicaldistancing measures than those in the wider population. This may be especially important at times and places where health systems risk being overwhelmed by cases. Other infection control measures include provision of personal protective equipment and intensive testing of health and social care workers in maximum contact with at-risk individuals. At a minimum, timely and effective communication should be provided to communities on who within them is at increased risk. Among those who are identified, governments will rely heavily on their adherence to guidelines. This would allow practical individual-level steps to be taken, such as increased hygiene, physical isolation and home-delivered food and medical care. 6 As more evidence emerges on the risk associated with different conditions, guidelines could be refined and shielding policies tailored to different risk groups e.g. isolation for those at very high risk, and less stringent measures (e.g. social distancing) for those with a lower level of increased risk. Community-level shielding approaches, including vacating houses or public buildings to physically isolate small groups of people at increased risk, may also be considered, though these will require stringent infection control arrangements, especially in crowded settings, 24 and adherence may be low if at-risk individuals are daily wage earners or people caring for children e.g. grandparents. 25 The association between the prevalence of underlying conditions and other national characteristics, such as economic development, is complex. The prevalence of many of these conditions (HIV/AIDS may be an exception) reflect the epidemiological transition 26 but survival with these conditions may reflect the performance of the health system. 27 Hence, it is important to look at the data for each country, which goes beyond what we can report in this paper. We provide a spreadsheet tool (available at https://cmmid.github.io/topics/covid19/) that can be used for rapid assessment (and visualisation) of the estimated number and percentage of country populations targeted under different shielding policies. This allows different health conditions to be included/excluded, different age thresholds to be assessed, and different choices about key assumptions e.g. estimates of the ratio , and the multimorbidity fraction by age. Prevalence data included in our spreadsheet can be updated as more evidence emerges on the importance (or otherwise) of specific conditions and their severities e.g. early stage CKD, simple hypertension etc.