Comparing Asthma Complications in COVID-19 With Flu

A research letter published in Annals of the American Thoracic Society has challenged US Centers for Disease Control and Prevention (CDC) assumptions that those with asthma are at higher risk for severe SARS-CoV-2 infection.

Research was led by Fernando Holguin, MD, MPH, of the Pulmonary Division at University of Colorado’s Anschutz Medical Campus.

People living with asthma often make up more than 20 percent of those hospitalized in the United States during the annual influenza season.

For SARS-CoV-2, several noteworthy risk factors for hospitalization such as hypertension, diabetes, chronic obstructive pulmonary disease, and obesity have been demonstrated.

Amid the outbreak of Middle East Respiratory Syndrome (MERS), there was sparse evidence asthma patients may be at higher risk.

But the underwhelming proportion of people with asthma among patients across several international studies raises questions about asthma as a particular risk factor when it comes to being hospitalized for coronavirus disease 2019 (COVID-19).

The study team examined asthma prevalence among patients hospitalized for COVID-19 reported in 15 studies with population asthma prevalence and a 4-year average of asthma prevalence in influenza hospitalizations across the United States.

The team further validated results with a cross sectional analysis of 436 COVID-19 patients admitted to the University of Colorado Hospital to assess the likelihood of intubation among people with asthma compared to non-asthmatics.

“The proportion of asthmatics among hospitalized patients with COVID-19 is relatively similar to that each study site’s population asthma prevalence. This finding is in stark contrast to influenza,” authors wrote.

“Seasonal coronaviruses typically do not contribute significantly to hospitalizations due to asthma exacerbations since they primarily cause upper respiratory infections. In the case of SARS-CoV (not COVID-19), asthmatics did not seem to be disproportionately affected, although minimal data is available to make this comparison,” the authors added.

In the 2019-2020 flu season, about 24% of people hospitalized with influenza had asthma. This is a far larger burden than the pooled prevalence estimate across the 15 COVID-19 studies (6.8% (95% confidence interval: [3.7, 10.7]).

“Despite early concern about disproportionately high morbidity and mortality for those with asthma, data presented here and elsewhere show minimal evidence of a clinically significant relationship,” the authors explain.

Why, though, might this be the case?

The authors offer a speculative answer as to why COVID-19 is not associated with greater hospitalization rates among people with asthma: it may depend on the distribution of the ACE2 receptor in the respiratory airway epithelium.

ACE2 is the human receptor that SARS-CoV-2 binds to.

Diabetes and hypertension are thought to potentially increase ACE2 expression.

On the other hand, authors theorize, inhaler-mediated corticosteroid administration may decrease ACE2 expression. Asthma patients with a predominantly allergic phenotype may have significantly lower expression of ACE2 regardless.

Authors cautioned that there is a need for further data derived from a larger sample size, and that patients with asthma can still get severe COVID-19. They simply may not acquire it much or any more than the rest of us.