Higher air pollution could be linked to increased deaths and cases of coronavirus in England, a preliminary study suggests.

An analysis by the Medical Research Council Toxicology Unit at Cambridge University compared regional data on total Covid-19 cases and deaths, against levels of three major air pollutants.

The study used data from seven regions in England, where a minimum of 2,000 infections and 200 deaths are reported from February to April 8, 2020, and air pollution records from more than 120 sites in 2018 and 2019.

Levels of pollutants nitrogen dioxide and nitrogen oxide, much of which comes from traffic fumes, were highest in London, the Midlands and the North West and lowest in southern regions of England.

Fatalities of people with the coronavirus, known as SARS-CoV-2, followed the same trend, the study found, suggesting the higher the pollution levels, the greater number of Covid-19 cases and deaths.

The researchers said their study provided evidence that higher levels of some air pollutants correlate with increased Covid-19 mortality and spread in England.

But other experts warned that the results did not show a causal link between poor air quality and worse Covid-19, adding disease transmission and death would be expected to be higher in highly-populated areas such as London, which also have higher air pollution.

Though most people with the virus have a mild illness, some patients go on to develop severe respiratory conditions, and scientists are trying to work out why some sufferers are more at risk of a serious response than others.

Previous studies have pointed to a higher risk for older people or those with underlying health conditions including cardiovascular disease, diabetes, chronic respiratory disease and cancer.

Long-term exposure to air pollutants from car exhaust fumes or burning fossil fuels can put people at risk of these health conditions, and can also increase the risk of infection by viruses that affect people’s airways.

This highlights the importance of reducing air pollution for the protection of human health

Marco Travaglio, a PhD student at the MRC Toxicology Unit, said: “Our results provide the first evidence that SARS-CoV-2 case fatality is associated with increased nitrogen oxide and nitrogen dioxide levels in England.

“London, the Midlands and the North West show the largest concentration of these air pollutants, with southern regions displaying the lowest levels in the country, and the number of Covid-19 deaths follows a similar trend.”

The researchers say that their findings, which have not yet been peer reviewed, only show a correlation between dirty air and more severe Covid-19 disease.

Further research is needed to confirm that air pollution makes Covid-19 worse, but it does chime with findings from other parts of the world including northern Italy and the United States.

Dr Miguel Martins, senior author on the study, added: “Our study adds to growing evidence from Northern Italy and the USA that high levels of air pollution are linked to deadlier cases of Covid-19.

“This is something we saw during the previous Sars outbreak back in 2003, where long-term exposure to air pollutants had a detrimental effect on the prognosis of Sars patients in China.

“This highlights the importance of reducing air pollution for the protection of human health, both in relation to the COVID-19 pandemic and beyond.”

Professor Keith Neal, Emeritus Professor of the Epidemiology of Infectious Diseases, University of Nottingham, said the study used the number of deaths rather than the death rate per population, which made larger cities look worse, such as London and Birmingham.

“Covid-19 around the world has affected areas with the greatest population densities to a much greater degree.

“The population density and more people to get infected could well explain their results rather than the direct effects of air pollution,” he said.