Long-term exposure to particulate matter (PM2.5) may increase the risk of contracting and dying from COVID-19 by up to 7%, according to researchers at the Office for National Statistics (ONS).
In order to understand the link between long-term exposure to air pollution and COVID-19, researchers at ONS developed a detailed statistical model controlling for factors such as levels of deprivation, ethnicity, population density, public health and pre-existing health conditions.
The researchers considered exposure to ozone, fine particulate matter (PM2.5) and nitrogen dioxide (NO2). They did not account for changes in pollution levels since the pandemic began.
At the start of the pandemic, infection rates were highest in cities where air pollution is also high.
Up to the week when lockdown began, 45% of deaths in England had occurred in London, however by the week ending June 12, this had fallen to 18%.
As the virus spread across the country, the correlation between air pollution exposure and COVID-19 mortality decreased.
While deaths rates have generally been higher in polluted areas, the researchers have highlighted that this on its own does not establish pollution as a cause of COVID deaths.
Using their statistical model, the researchers compared death rates among populations of similar health with the main difference being long-term exposure to air pollution.
Higher COVID-19 death rates have been widely recorded in Black, Asian and Minority Ethnicity (BAME) communities.
Ethnicity is strongly correlated to pollution exposure, with ethnic minorities more likely to live in polluted areas.
Without controlling for ethnicity, the researchers found that long-term exposure to the PM2.5 could increase the risk of contracting and dying from COVID-19 by up to 7%.
However, when controlling for ethnicity, the researchers found that air pollution exposure has no statistically significant impact on COVID-19 deaths.
As air pollution is just one of many factors that could be driving disproportionate outcomes for minority ethnic groups, the increased risk of dying from COVID-19 (found when ethnicity is not controlled for) is likely to be an overestimate of the true effect.
The researchers have said that although their research suggests that there is a link between air pollution and COVID-19 they have highlighted that this evidence is inconclusive.
They only examined air quality and COVID-19 deaths at the population level, based on the availability of existing data. At this level, they have to make assumptions such as consistent exposure to pollution across a 1km grid square.
In reality, exposure could vary from one end of a street to another, and individual exposure is affected by where someone works as well as where they live.