Underlying illnesses and the risk of severe Covid-19, if infected - what a modelling study shows

  • More than 1 billion people worldwide are at increased risk of developing severe Covid-19
  • However, not all of these infected individuals would require hospitalisation
  • A study could be used to help governments control the pandemic

The number of coronavirus cases and Covid-19 deaths continue to rise worldwide, but it is a select share of the population that may be at greater risk. This is according to a recent modelling study, carried out by a team of 16 researchers and published in The Lancet Global Health journal, using data from 188 countries.

The study proposed that one in five of the world’s population – an estimated 1.7 billion people, (22% of the world’s population) have at least one underlying health condition that could increase their risk of severe Covid-19, the disease caused by SARS-CoV-2, in the event that they do become infected. 

African countries with high HIV/Aids prevalence at risk

The authors’ results were based on disease prevalence data from the Global Burden of Diseases, Injuries and Risk Factors Study (GBD) 2017; UN population estimates for 2020; and the list of underlying health conditions relevant to Covid-19 (according to official current guidelines).

According to the study’s results, the following populations are at increased risk of severe Covid-19 (with at least one underlying health condition linked to Covid-19):

  • Countries with ageing populations
  • African countries with high HIV/Aids prevalence
  • Small island nations with high diabetes prevalence

The World Health Organization (WHO) indicates that there were around 37.9 million people living with HIV at the end of 2018, and that over two thirds (25.7 million) of all people living with HIV live in the WHO African Region.

Not all will develop severe Covid-19

However, the researchers also explained that not all people with these conditions would go on to develop severe symptoms if infected with Covid-19. Their findings reveal an estimation that 4% of the world's population – 349 million of 7.8 billion people – would require hospitalisation if infected. This means that the increased risk of severe disease could, in fact, be relatively low for those with underlying conditions.

Differences between countries

In an effort to understand the number of separate estimates of the proportion of all people, with and without underlying conditions, who would require hospitalisation if infected, the research team delved even further.

They found that countries and regions with younger populations have fewer people with at least one underlying health condition, while those with older populations have more people with at least one condition. To put this into context, the proportion of the population with one or more health conditions ranges from 16% in Africa (283 million people out of 1.3 billion) to 31% in Europe (231 million out of 747 million).

However, Associate Professor Clark points to the fact that the results should not lead to complacency about risk in Africa: "The share of the population at increased risk of severe Covid-19 is generally lower in Africa than elsewhere due to much younger country populations, but a much higher proportion of severe cases could be fatal in Africa than elsewhere."

What are the underlying medical conditions?

While there is still limited information regarding Covid-19, WHO identifies certain risk factors for severe disease. These include cardiovascular disease (including hypertension), diabetes, chronic kidney disease, chronic respiratory disease and cancer, among others.

The researchers focused mainly on underlying chronic conditions, and excluded other possible risk factors for Covid-19 that have not yet been added to the official guidelines, such as ethnicity. This, therefore, means that the figures should be treated with caution, but could be used as a starting point to help provide governments with an idea of the numbers that should be prioritised for protective measures, such as physical distancing and a vaccine (should it become available).

"As countries move out of lockdown, governments are looking for ways to protect the most vulnerable from a virus that is still circulating. We hope our estimates will provide useful starting points for designing measures to protect those at increased risk of severe disease.

“This might involve advising people with underlying conditions to adopt physical distancing measures appropriate to their level of risk, or prioritising them for vaccination in the future," Lead author and Associate Professor Andrew Clark from the London School of Hygiene & Tropical Medicine said.

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