• Scientists say twin studies illuminating possible genetic influence of COVID-19 must be interpreted with caution
  • Immune response to COVID-19 differs from other respiratory infections
  • Evidence mounts for air pollution link to severity of illness

Twin studies should be interpreted with caution

A recent (unpublished) study comparing the symptoms of identical and non-identical twins infected with COVID-19 concluded that COVID-19 symptoms appear to be around 50% genetic. The findings were based on data collected from over 2,600 twins via the COVID-19 Symptom Tracker app developed by a team at King’s College London.

Scientists not involved in the study have told the public to exercise caution when interpreting the findings from this and other studies of siblings, because it can be hard to tease apart environmental and genetic influences on disease outcome, particularly if people live in the same household. Scientists also warn that media coverage of twin deaths can also distort public perceptions of risk via a psychological effect known as salience bias, where we put too much emphasis on what we find striking.

Abnormal immune response to COVID-19

As we have seen in the past two months, not all comparisons between the current coronavirus, SARS-CoV-2, and other respiratory illnesses like the flu, are helpful. Yet, scientists continue to learn more about the virus by researching its similarities and differences to better understood viruses.

This week, scientists at the Icahn School of Medicine at Mount Sinai in New York discovered that cells infected with SARS-CoV-2 produce unusually low levels of antiviral proteins called interferons compared with cells infected with other respiratory viruses. At the same time, levels of proteins that activate more general immune responses were higher in infected individuals than healthy people.

Taken together, the findings, soon to be published in the journal Cell, suggest an immune imbalance, that could explain the unique signature of the disease: low levels of interferons reduce a cell’s ability to stop the virus replicating itself and the activation of less-specific immune responses promotes inflammation.

The study supports the idea that treatments targeting the immune system could help people with COVID-19.

Could air pollution be making COVID-19 worse?

It’s not gone unnoticed that some of the worst-hit areas, such as northern Italy, are also highly polluted, and several studies are starting to point towards air pollution amplifying the severity of COVID-19.

“We don’t have the evidence linking directly to mortality yet, but we know if you are exposed to air pollution you are increasing your chances of being more severely affected,” said Dr María Neira, Director of Public Health at the World Health Organization (WHO).

Preliminary studies show that air pollution could be important in three ways:

  • Death rates are higher in heavily polluted areas because individuals’ heart and lungs are already weakened by dirty air.
  • Pollutants inflame the lungs potentially making people more likely to catch the virus.
  • Pollution particles might help carry the virus further.
A combination of two animated images show the fluctuation of nitrogen dioxide emissions across Europe from January 2020 until March 11, 2020. New data from the Copernicus Sentinel-5P satellite reveal the decline of air pollution, specifically nitrogen dioxide emissions, over Italy.  This reduction is particularly visible in northern Italy which coincides with its nationwide lockdown to prevent the spread of the coronavirus, in this handout obtained by Reuters on March 13, 2020. European Space Agency
New data from the Copernicus Sentinel-5P satellite reveal the decline of air pollution, specifically nitrogen dioxide emissions, over Italy.
Image: European Space Agency

None of these studies have yet been peer-reviewed and researchers caution against implying causation from the correlation between air pollution and severity of COVID-19. The main risk of catching COVID-19 is still being in contact with an infected person but further research into the role that air pollution plays could help to better respond to the pandemic, especially as many countries are beginning to lift lockdown measures.