Written by Debbie Lambert — Fact checked by Alexandra Sanfins, Ph.D.
A large, population-based study from the United Kingdom suggests that there is limited overlap between the risk factors for developing COVID-19 and those for developing severe disease.
The findings appear in the respiratory journal Thorax.
After the researchers adjusted for factors that could influence exposure to SARS-CoV-2, Asian or Asian British ethnicity and high BMI were associated with a higher risk of developing COVID-19.
They also found that atopic conditions — such as asthma, eczema, and hay fever — were associated with a decreased risk of developing COVID-19. Atopic conditions are allergic diseases. For example, atopic asthma is asthma that is triggered by an allergen.
Valuable information
Although much is known about severe COVID-19, researchers have not studied risk factors for milder COVID-19 in as much detail.
However, understanding what makes people more susceptible to infection can provide valuable information about how COVID-19 develops and spreads. This knowledge could help protect those at risk of severe disease.
The researchers, who are from institutions across the U.K. but primarily based at Queen Mary University London (QMUL), carried out a population-based study to find out more. The study followed 15,227 participants from May 2020 to February 2021.
The participants completed a baseline questionnaire on potential symptoms of COVID-19 and the results of any COVID-19 tests they had taken.
The team also collected details of potential risk factors, including information on:
- sociodemographic factors
- occupation
- lifestyle
- weight
- height
- medication use
- vaccination status
- diet and supplementation
- long-term medical conditions
Monthly follow-up questionnaires captured test-confirmed SARS-CoV-2 infection along with potential COVID-19 symptoms.
During the study, there were 446 cases of COVID-19. This means that almost 3% of the participants who completed the study developed the disease.
The following were all linked to an increased likelihood of developing COVID-19:
- household overcrowding
- visits with other households during the previous week
- visits to indoor public places
- frontline occupations, excluding health and social care
- Asian or Asian British ethnicity
- raised BMI
After adjusting for factors that influence exposure to SARS-CoV-2, Asian or Asian British ethnicity and high BMI were still associated with increased odds of developing COVID-19.
Atopic disease was associated with decreased odds, particularly among people with asthma.
The study found that there were no associations with age, sex, other medical conditions, diet, or supplement use.
Lead researcher Prof. Adrian Martineau is a professor of respiratory infection and immunity at the Institute of Population Health Sciences at QMUL.
He told Medical News Today that he was surprised by the results: “We did not anticipate that people with allergies and allergic asthma would have a lower risk of developing COVID-19 — in fact, there was a concern early in the pandemic that people with [airway diseases] would be at heightened risk.”
“Our finding of reduced COVID-19 risk in this group may reflect lower levels of expression of ACE-2 in people with allergic disease — since ACE-2 is the receptor for SARS-CoV-2.”
– Prof. Adrian Martineau
SARS-CoV-2 enters human cells by binding to the ACE-2 receptor on cell surfaces. Earlier research suggested that people with allergic asthma express less of the ACE2 gene — which encodes the ACE-2 receptor — in their airway cells.
Prof. Martineau told MNT, “We saw that increased risk of COVID-19 in people of Asian ethnic origin was not explained by any socioeconomic, occupational, or comorbid factors investigated. This is an important finding, [and it] underlines the need for further research to understand reasons for ethnic differences in susceptibility to COVID-19.”
The authors point out that there are some limitations to this study.
Firstly, there was no oversight of swab testing. Instead, the study relied on the results of routine testing, which symptoms usually would have prompted. So, the study may have missed those with symptomless infections.
Secondly, participants all volunteered to take part. The study authors explain that some ethnic minorities — particularly Black, African, and Caribbean ethnicities — were underrepresented in the study.
Prof. Martineau added, “Regrettably, people of Asian and Black ancestry were underrepresented in the cohort, despite our best efforts to recruit a representative sample of the U.K. population. This may compromise generalizability of our findings.”
“However, we have no a priori reason to believe that risk factors we identified — such as obesity, household overcrowding, and socializing indoors with other households — would apply differently to people of different ethnic/racial origin[s].”
Further work
The results point to a need to further investigate the social and biological factors that might explain ethnic disparities in the risk of developing COVID-19.
“One factor of particular interest is vitamin D deficiency,” Prof. Martineau told MNT. He added: “[This] is known to be more common in people of Asian and Black versus white ancestry in the U.K. Vitamin D has been shown to boost immunity to other respiratory pathogens, so we are doing a randomized controlled trial of vitamin D supplementation to reduce [the] risk and severity of COVID-19 in 6,200 U.K. adults.”
“Our finding of increased disease risk associated with socializing indoors with other households supports the rationale for limiting social contact as a method to control disease when new variants of concern arise if they are not being controlled by vaccination or other public health measures.”
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