Photo/Illutration A new face mask stamp used by asthma patients alerts people around them that they are coughing because they have asthma, not the novel coronavirus. (Provided by Okada Shokai Co.)

Contrary to a popular assumption, bronchial asthma is unlikely to increase the severity of symptoms of the novel coronavirus, according to a study by the National Center for Child Health and Development (NCCHD) in Tokyo.

The team announced its findings on COVID-19 patients in other countries on its website on June 2. The results were also published in a U.S. medical journal.

When asthma patients catch a common cold, they are said to be more prone to asthma attacks as they cannot sufficiently produce the proteins that destroy the virus.

There were fears that such people might be at higher risk of developing severe symptoms of COVID-19.

The research team analyzed data from published studies on around 2,200 coronavirus patients in China and the United States whom the team was able to determine a correlation between the severity of COVID-19 symptoms and pre-existing health conditions.

The results showed 4.1 percent of the coronavirus patients with mild symptoms had asthma, while 5.5 percent of those with severe symptoms suffered from asthma, showing no statistically significant difference.

However, COVID-19 patients with diabetes or chronic obstructive pulmonary disease (COPD) were more likely to develop severe symptoms of the coronavirus, according to the study.

Of those with mild symptoms, 6.7 percent had diabetes, while the figure jumped to 25.0 percent among severe patients. COPD patients accounted for 1.5 percent of mild patients, but the number increased to 6.5 percent of severe patients.

The virus that causes the common cold or influenza enters the body mainly through the nose or throat and binds to a receptor of a cell to infect the person. The novel coronavirus is known to attach to a different receptor from the one that the cold and flu virus does.

The team noted that recent basic research reported an increase in the amount of proteins produced from allergic reactions that induce asthma reduces the expression of a receptor that the novel coronavirus binds to. That may explain the team's finding that asthma does not significantly increase the severity of COVID-19 symptoms, the researchers said.

“Our latest study presented only epidemiological data, so more studies are needed to determine the causal relationship (between the severity of COVID-19 symptoms and pre-existing conditions),” said Kenji Matsumoto, who heads the NCCHD’s Department of Allergy and Clinical Immunology.

“But people with asthma do not need to worry too much that their health condition could aggravate symptoms of the coronavirus.”

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