[Reading Science] Why Did I Feel Worse Even Though We Had the Same COVID-19?

Scientists' Solution
Immune Response and Inflammation Vary by Individual
"High Immunity + Low Inflammation = Longevity"

Everyone can be infected by viruses. However, the effects vary greatly. For example, even when infected with the same COVID-19 virus, some people remain asymptomatic or recover easily, while others may even die. This is due to significant individual differences in the human immune system. Recently, scientists have attracted attention by publishing research results indicating that these individual differences are due to variations in immunity and inflammatory responses. In particular, strong immunity combined with low inflammatory responses is directly linked to longevity, and preventive measures such as wearing masks, weight control, and exercise are advised as the best methods.

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The following is an interview conducted by the American scientific media Scientific American on the 21st of last month with Sunil Ahuja, a professor at the University of Texas Medical School and the author of the relevant paper.

- Why are certain people more vulnerable to diseases?

▲ Generally, there are three factors to consider regarding vulnerability to diseases. The first is genetic susceptibility. Some people are born with genetic factors that make them more prone to diseases. The second is the environment. Our ancestors, who lacked vaccines or hygienic living conditions, mostly died by their 50s due to inflammation stress caused by infections.

The third is that each person responds differently to inflammation stress. People respond differently when infected by various viruses. The problem is that immune responses expressed to protect the body from one virus infection can be harmful in the case of another virus infection. People show diverse reactions when faced with such issues, which may be due to genetic causes. When fighting viruses, some inflammation occurs, but it must be appropriate. Injured or infected areas swell, turn red, and become hot. This inflammatory response signals that white blood cells must prevent further spread of inflammation and promote healing. The body produces chemokines, substances that attract white blood cells.

However, some people experience excessive inflammation, while others have insufficient inflammatory responses, showing various differences among individuals. In this study, we revealed that the ability to regulate inflammation and preserve immunity is related to being asymptomatic. Certain individuals have excellent inflammatory response capabilities, so they do not develop symptoms even when infected by viruses.

- For example, people in certain professions, such as teachers, get sick more often. Why is that?

▲ First, it is somewhat related to the amount of microbes. Teachers conduct classes in enclosed spaces with 30 to 40 children, exposing them to large amounts of viruses. The same applies to daily childcare workers. The more exposure to viruses, the higher the possibility of immune function decline. In other words, the issue is how inflammation and the effective immune system that responds well to it are strengthened or weakened. This cycle progresses according to the drivers of life and life stages. Some maintain strong immune systems even as they age, while others gradually weaken. Especially, some individuals have a tendency for immune system function to decline easily regardless of age.

- How much does immune resilience affect longevity?

▲ People can be classified into four groups. Those with high immunity and low inflammatory responses live the longest. Conversely, those with low immunity and strong inflammatory responses unfortunately die earlier than others as they age. Those with both low or both high immunity and inflammatory responses tend to live an intermediate lifespan.

- What is the way to prevent fatal infections?

▲ It is similar to the question of how to avoid being robbed when going to a store. Even among very healthy people, some die from the flu. Having healthy immunity does not guarantee protection from infection by certain viruses. Even young people with poor immunity can get infected despite vaccination. The best approach is to protect oneself from exposure to viruses with a high risk of infection.

- Then, what are those methods? How can the risk of exposure to dangerous pathogens be reduced?

▲ I am always glad to see elderly patients wearing masks while walking in hospital yards. It means they understand the basic principle of coping when immunity is weak, have received relevant information, and are trying to protect themselves. Weight loss and exercise are also important. People who exercise continuously and steadily have strong immunity. These are all important factors in human behavioral changes that can reduce disease risk. Changing human behavior is very difficult. What I want to emphasize is that to prevent disease risk, common-sense preventive measures such as wearing masks and behavioral corrections like exercise and weight loss must be practiced.