COVID-19 and asthma
Observational studies indicated a potential protective factor of asthma
for the morbidity and mortality of COVID-191,50,
although conflicting data from the United States and United Kingdom (UK)
suggested a higher prevalence of asthma in COVID-19
patients106. A UK study found that asthmatic patients
were associated with a higher risk of COVID-19107. For
allergic asthma, the protective effects have been partly attributed to
the antiviral effect of eosinophils35, whose
beneficial effects on COVID-19 outcomes depend on
ICS108. However, whether COVID-19 patients with asthma
are at higher risk of long-COVID symptoms is still unclear as there are
contradictory research studies109,110.
It remains unclear whether asthma is a risk factor for the severe and
worse outcome of COVID-19. However, it appears to be related to the
asthma phenotype, treatment and severity111,112.
Asthma was shown to be associated with an increased hospitalization risk
of COVID-19 both in adults50 and in
children113. Another study observed an increased
hospitalization rate only in asthmatic patients needing regular ICS or
regular/intermittent ICS with add-on therapy107. The
hospitalization rate of allergic asthmatics was 50% lower compared to
non-allergic asthmatics110. A recent meta-analysis
identified preexisting asthma as a risk factor for intensive care unit
(ICU) admission among COVID-19 patients114. The
heterogeneity of asthma endotypes (allergic vs. nonallergic asthma) may
underly the different disease course in these
studies35,110. Eosinopenia was associated with worse
outcomes of COVID-19, including longer duration of hospitalization,
higher severity and mortality1,36,110. Dynamic
monitoring of eosinophils counts in addition toother laboratory indices,
such as neutrophil-to-lymphocytes ratio lymphocytopenia and D-dimer, may
be used as predictive biomarkers of the outcomes of
COVID-1935,36. Biologicals were associated with lower
susceptibility in asthmatic patients115. Omalizumab
augmented IFN-α production from plasmacytoid dendritic
cells116, which may also contribute to the protecting
effects of asthma against COVID-19.
A lower expression of ACE2 in bronchial epithelial or lung tissue was
observed in allergic asthmatic patients106,117,118. In
addition, ICS may decrease the expression of ACE2 and TMPRSS2 in
bronchial epithelia of asthmatic patients59 and thus
contribute to lower susceptibility to infection. The current evidence
does not indicate an increased risk of long COVID-19 in asthmatic
patients, although studies with more patients are
warranted118. The symptoms of long COVID-19 are
summarized in Table 2.
Table 2.Reported symptoms of
post-acute COVID-19 syndrome or long COVID-19.