It is a common perception among doctors and public that, asthma may predispose to severe form of Corona Virus Disease 2019(COVID 19).

Corona Virus infects primarily the respiratory tract and Asthma is the most common chronic  disease of  respiratory tract worldwide.

The primary symptoms of Asthma are cough and breathlessness ,which are also the symptoms of Corona Virus Disease 2019.

Asthma is an allergic disease of airway in most of the cases in children ,whereas COVID 19 is an infective disease.

Viruses,chiefly Rhinovirus and Respiratory Syncytial Virus(RSV) are the trigger factors for asthma exacerbation.

So,it is presumed that Corona Virus can also trigger asthma and both may cause serious condition.

Since the airway epithelium and leucocytes of persons suffering from asthma have impaired production of antiviral interferons(Interferon alpha,beta,gamma),due either to allergic inflammations or primarily,it was presumed that the innate immunity of these individuals can not check the viral infections from travelling to lower respiratory tract form upper respiratory tract.

Literature search from 8 studies,comprising more than 17ooo individuals form different geographical areas revealed that the prevalance of COVID 19 was low in areas where prevalance of asthma was high .In persons having comorbidities like Diabetes Mallitus and COPD,Corona Virus infection caused severe infections which was not seen in comorbidities like Asthma.

According to a research,it has been found that 2 host molecules are important for severe acute respiratory syndrome corovirus 2(SARS COV 2).Corona Virus uses ACE 2 receptor (angiotensin converting enzyme 2 receptor) to enter the cell and transmembrane serine protease for priming of S protein  of the virus.

In vitro treatment of epithelial cells with interferons increased the expression of ACE 2 receptor.

The high level of interleukin 13 and T2 cytokines  downregulate the expression of ACE2 in epithelial cells.

Asthmatic individuals have high levels of T2 cytokines and interleukin 13.

Bronchial epithelium of asthmatic individuals have low expression of ACE2 receptor as compared to general population,whereas persons having severe form of COVID 19 show high level of interferon.

Researchers concluded that Asthma may be a protective factor for COVID 19 as asthmatic respiratory epithelium shows low expression of ACE2 receptor.

The study is published in Journal of Allergy and clinical immunology.

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