A study of 105 protective and risk factors related to the incidence and severity of COVID-19

Some of the different risk factors that have been associated with an increased risk of severe coronavirus disease 2019 (COVID-19) or mortality include comorbidities such as cardiovascular diseases, hypertension, diabetes, and chronic respiratory diseases. To date, few studies have looked at other risk or protective factors associated with symptomatic and asymptomatic COVID-19.

A recent study published on the preprint server medRxiv* discusses a systematic investigation of both the known and unknown factors that may affect the risk of infection with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus responsible for COVID-19,  and a severe course of COVID-19.

Study: Effects of 105 biological, socioeconomic, behavioral, and environmental factors on the risk of SARS-CoV-2 infection and a severe course of Covid-19: A prospective longitudinal study. Image Credit: Drazen Zigic / Shutterstock.com

About the study

Here, the researchers conducted a large prospective longitudinal study on 5,164 subjects in the Czech Republic who did not have a history of COVID-19 prior to the fourth surge of cases in this nation. Among the 5,164 responders, 1,746 were male and 3,411 were women, whereas 7 subjects did not answer the question about their sex. These subjects shared their information online about their exposure to 105 different risk factors.

At the time of the study, 13.7% (709) of subjects contracted SARS-CoV-2, whereas the remaining 86.3% (4,455) did not. Women were comparatively less infected than men, with this difference being more significant when controlled for age and urbanization. Both men and women who had COVID-19 reported suffering physically and mentally to a greater extent as compared to those who escaped infection.

To determine the biological, socioeconomic, behavioral, and environmental factors influencing the risks of SARS-CoV-2 infection and severe COVID-19, the researchers used separate partial Kendall correlation tests controlled for age, sex, and urbanization level with factors as independent factors, and dependent variables including infection with SARS-CoV-2, the course of COVID-1, the severity of symptoms index, length of infection, and physical and mental health indices.

The protective or risk factors

The 105 potential protective and risk factors investigated in this study included sex, age, body mass index (BMI), blood group, Rh positivity, urbanization, members of the household, education, family income, children, face mask use, hand washing, maintaining a safe distance, food habits, sports, vitamins, walking in nature, animals, depression, diseases, and use of herbs, among others.

Broadly, researchers grouped these factors into five categories, which included:

  • Biological factors including morphological traits
  • Sociodemographic factors
  • Behavioral traits/lifestyle variables
  • Contacts with animals
  • Comorbidities
  • Use of vitamins and supplements.

Study findings

While individuals with higher weight and higher BMI values experienced a more severe course of the disease, taller and heavier men also had a higher risk of infection as compared to shorter and less heavy men. Interestingly, the study found that the association between infection and height was stronger than the association of infection with weight or BMI. This observation was not found in women.

The researchers also observed that the risk of infection was lower in men and older subjects. This correlation is possibly due to the efforts of people who considered themselves at risk to avoid possible sources of infection. This is similar to the findings in subjects with other risk factors such as immunodeficient syndromes or chronic obstructive pulmonary disease.

The authors of the current study also found that moderate risks of COVID-19 infection were associated with the blood group (system ABO); however, no effect of the blood group or the Rh factor was reported on the severity of COVID-19.

“Our results indicate that potential effects of Rh factor on the risk and severity of Covid-19 do deserve further attention, but investigation of this phenomenon should be preferably based on DNA-genotyped populations because Rh-positive heterozygotes have better and Rh-positive homozygotes worse health than Rh-negative individuals.”

The sociodemographic factors mostly agreed with previously published data and were found to have had moderate effects on the risks of COVID-19. Notably, pets (dogs and cats) had no effect on the risk of infection and of severe COVID-19, despite previous studies showing the risk of viral transmission through animals.

Although all medical care, except for non-essential dentistry procedures, is paid for from mandatory medical insurance in the Czech Republic, higher-income individuals likely invested more in disease prevention, as their income positively correlated with their mental and physical health.

In the current study, the researchers found that being actively involved in a sport and cold-water swimming increased the risk of infection. This is comparable to other studies that have shown physical inactivity to be a risk of COVID-19. The researchers concluded that this association likely indicates that physical activity is a risk factor for SARS-CoV-2 infection, but not for severe COVID-19.

Conforming to previous observations, the strongest protective factor against COVID-19 infection was strict adherence to wearing masks and respirators, with the second strongest protective factor being the consumption of vitamins and supplements. However, anxiety and depression, especially among women, posed a risk of acquiring infection.

Interestingly, the researchers found an unexpected and strong protective effect against infection and severe COVID-19 in those diagnosed with borreliosis in the past or who reported drinking rooibos. The immunoregulative activity of the extracellular parasite Borrelia might confer immune protection against SARS-CoV-2 and a cytokine storm.

Rooibos, which is not a medical-herb drink, is a fermented extract from the leaves of Aspalathus Linearis. This drink has both antioxidant and anti-inflammatory properties, both of which may play a role in its protective effects against SARS-CoV-2. To date, there is no data relating to rooibos and COVID-19.

*Important notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:
Dr. Ramya Dwivedi

Written by

Dr. Ramya Dwivedi

Ramya has a Ph.D. in Biotechnology from the National Chemical Laboratories (CSIR-NCL), in Pune. Her work consisted of functionalizing nanoparticles with different molecules of biological interest, studying the reaction system and establishing useful applications.


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