The severity of COVID-19 can vary hugely. In some it causes no symptoms at all and in others it’s life threatening, with some people particularly vulnerable to its very severe impacts.

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The virus disproportionately affects men and people who are older and who have conditions such as diabetes and obesity. In the UK and other western countries, ethnic minorities have also been disproportionately affected.

While many factors contribute to how severely people are affected, including access to healthcare, occupational exposure and environmental risks such as pollution, it’s becoming clear that for some of these at-risk groups, it’s the response of their immune system – inflammation – that explains why they get so sick.