People with asthma are around 30% less likely to contract Covid-19, an Israeli study has concluded.
Tel-Aviv University researchers looked at 37,469 people tested for coronavirus and found among the 2,666 participants who tested positive 6.75% (153) also had asthma. This compared to 9.62% (3,388) who had asthma among the 34,803 who tested negative for the virus.
After adjusting for sex, age, smoking, and comorbidity factors, the team calculated people with asthma were 29% less likely to test positive.
The study stated: ‘The preexisting diagnosis of asthma had a statistically significant negative association with the likelihood of Covid-19 infection.’
The authors suggested that inhaled corticosteroids – used to treat asthma – could protect patients with asthma by reducing airway inflammation but stressed they found no evidence for it.
Another theory is centered around an enzyme called ACE2, which is the entry receptor for Covid-19, as ACE2 levels are reduced in respiratory conditions such as asthma.
But the relationship between asthma and coronavirus should be studied further, as it has not been ‘adequately documented’ despite being common in the population, the authors added.
Other studies have also shown a low prevalence of Covid-19 among people with asthma.
For example, the China Center for Disease Control reported in February that only 2.4% of 44,672 patients with COVID-19 had chronic respiratory diseases, including asthma.
And in previous severe acute respiratory syndrome (SARS) outbreaks, research has found that people – and particularly children – with asthma appeared to be less susceptible to infection.
In August, a French study found that patients with asthma do not seem to be at risk from complications associated with being hospitalised with Covid-19.