Our findings show the mortality risk for these vulnerable groups increases significantly and could lead to thousands of avoidable deaths.
Lifting the coronavirus lockdown could lead to tens of thousands extra deaths, new research has suggested.
Scientists at University College London (UCL) estimate there could be anything between 37,000 and 73,000 excess deaths within a year due to the Covid-19 pandemic, but that depends on how restrictions are lifted.
They built a risk calculator taking things such as age, sex and underlying illnesses into account.
The data takes into account the risks of the infection as well as indirect effects such as strain on the health service.
Author Professor Harry Hemmingway said keeping the infection rate down among the public is helping to keep vulnerable people safe.
So far, lockdown measures have pushed the 'R' rate of the illness - the rate of transmission - below one.
He explained doctors also "need to continue to deliver high quality medical care to vulnerable people to prevent excess deaths in those who are not infected with coronavirus".
The study, published in The Lancet journal, looked at data from 3.8 million health records and based its conclusions on England having a 10 percent infection rate and 20 percent of people having a high-risk condition.
Lead author Dr Amitava Banerjee explained: "For example, we show how a 66-year-old man with chronic obstructive pulmonary disease has a six percent risk of dying over the next year and there are 25,000 'patients like me' (i.e. men of the same age with the same condition) in England.
"The calculator estimates 164 excess Covid-related deaths on top of the expected 1,639 deaths over a year in patients in a similar situation."
He added: "Our findings show the mortality risk for these vulnerable groups increases significantly and could lead to thousands of avoidable deaths."
Another author said the data could help inform NHS policy on vulnerable patients.
Professor Hemmingway explained: "Our findings emphasise the importance of delivering consistent preventive interventions to people with a wide range of diseases, who are cared for by a wide range of clinical specialties.
"This policy is only possible because we have an NHS able to use system-wide data for patient benefit."
Caitlin Doherty is a reporter with PA.