Why COVID-19 Affects Different People in Different Ways

One of the confounding things about the coronavirus is the wide range of disease severity that infected people experience. Whilst a minority of patients with the disease require hospitalization, for these patients the effects can be severe and, in some cases fatal. Other people have mild symptoms or none at all. Understanding why some patients suffering from COVID-19 become severely ill, while others do not, could help to inform how to prevent and treat the disease, as well as helping to shape public policy in the short and long term.

Let’s look at some of the factors affecting the severity of the infection.

Age – Middle aged and older patients are far more likely to suffer symptoms, to be hospitalized and to die than young people. Analysis of Chinese data estimates the chance of death in COVID-19 cases is more than 13% for patients 80 and older, compared to about 0.15% for patients in their 30s, and virtually 0% for patients under 20. A study of early U.S. cases by the Centers for Disease Control and Prevention (CDC) had similar findings (1).

It is known that older immune systems tend to be less efficient at clearing viral infections. However, it seems that COVID-19 affects people in their 40s, 50s, and 60s far worse than other viral infections, such as flu. Research in Georgia in the USA found that out of 305 hospitalized patients with COVID-19, 60% were less than 65 years old (2).

Immune System – Severe COVID-19 is driven not just by viral damage to cells but by an inflammatory storm that causes damage to the lungs and other organs. It may be that the immune system of middle aged people is less efficient at dealing with this than younger people’s. It may also be that children who get COVID-19 may be less likely to develop an inflammatory storm (1). It is likely that the varying immune response, complex inflammatory reactions, and the interplay with bacterial co-infections, the vascular system and micro-circulation throughout the body may all play a part (3).

Gender – Whilst roughly equal numbers of men and women appear to become infected with COVID-19 in most countries men are more likely to die from it (2). There may be many reasons for this difference including differences in the immune response of men and women. Additionally lifestyle factors may play a part; men are more likely to drink alcohol and smoke tobacco, both of which weaken the immune system. Smoking also increases inflammation and susceptibility to respiratory infections.

Underlying Health Problems – Patients who develop serious or fatal COVID-19 are more likely to have at least one major underlying health condition, such as diabetes, hypertension, obesity, cardiovascular disease, asthma, kidney disease or chronic obstructive pulmonary disorder (1).

Many of these conditions are associated with weaker resistance to infections. Patients with conditions such as asthma may use immune suppressing drugs which increase their susceptibility to respiratory infections. Long term use of non-steroidal anti-inflammatory drugs, such as ibuprofen, for chronic conditions such as arthritis is known to affect kidney function. Patients taking immune suppressing drugs for cancer or organ transplants often have weakened immune systems.

That said, the research into patients hospitalised with COVID-19 in Georgia found that just over a quarter of patients did not have any underlying conditions (2). 

Ethnic Group – There is emerging evidence that African Americans are more likely to develop severe COVID-19. Research in Georgia found that 83% of patients hospitalised with COVID-19 were black (2). There may be many reasons for this including socio-economic factors, living in high density housing and the relatively high rates of underlying health problems in African Americans. Genetic factors in different ethnic groups may also contribute to disease severity and treatment response (4).

Genetics – Some apparently healthy people may have inherited immune system features that leave them more vulnerable to infection. This may be due to random genetic variation as well as ethnicity. Populations with less historical exposure to previous coronaviruses could also be more vulnerable to COVID-19. 

Viral Load – The amount of exposure to an infectious agent can affect the severity of the disease. Catching a high dose from a very sick patient is likely to increase the risk of developing severe illness compared to catching a low dose from a mildly symptomatic person.

Viral strain – COVID-19 is caused by a single-stranded RNA virus that has the ability to mutate quickly. At the moment there is no evidence that there is much variation in the viruses that cause COVID-19. Over time, and as it spreads around the world, it may develop genetically distinct strains, some of which may spread more easily, or cause more severe disease (1).

Diet – Some foods contain antioxidants, vitamins and minerals that support the immune system while other dietary components are known to have a negative effect on immune health, inflammation and lung health. For example, animal studies demonstrate that a high intake of resveratrol may have a protective role when it comes to the severity of infection with coronavirus, whereas a high intake of dietary fat may have a detrimental role (5). More research needs to be done on the effects of specific dietary components but diet should certainly be considered as part of the plan for prevention and treatment of the disease.

Unknowns

As yet there is much we don’t know or understand about the novel coronavirus and why some people are more severely affected than others. Over time these unknowns may be revealed. In the mean time it’s worth remembering that we are all at risk, one way or another, of both succumbing to the illness, and of spreading it to others (2).

Whilst some of the factors above are beyond our control one thing we can do to protect ourselves is to support our immune systems with a healthy diet and lifestyle. See blog posts on The Importance of Nutrition for the Immune System and Supplements for the Immune System for more information about how we can protect our immune systems.

References

1. Cornell Chronicle. Why is COVID-19 mild for some, deadly for others? Schnabel J. April 20, 2020

2. Morb Mortal Wkly Rep. 2020 May 8;69(18):545-550.Characteristics and Clinical Outcomes of Adult Patients Hospitalized with COVID-19 – Georgia, March 2020. Gold JAW et al.

3. Cardiol J. 2020 May 7. [Epub ahead of print] COVID-19 – toward a comprehensive understanding of the disease. Kowalik MM et al.

4. J Cosmet Dermatol. 2020 Apr 25. Racial Variations in COVID-19 Deaths May Be Due to Androgen Receptor Genetic Variants Associated with Prostate Cancer and Androgenetic Alopecia. Are Anti-Androgens a Potential Treatment for COVID-19? McCoy J et al.

5. Am J Physiol Endocrinol Metab. 2020 May 1;318(5):E830-E833. Biological plausibility for interactions between dietary fat, resveratrol, ACE2, and SARS-CoV illness severity. Horne JR, Vohl MC.