Asthma protects against severe cases of Covid, suggests study – 03/30/2023 – Equilíbrio e Saúde


Since the beginning of the pandemic, in 2020, it has been speculated that asthma could contribute to the worsening and lethality of Covid-19. Recently released in the journal Frontiers in Medicine, the results of the largest study carried out so far with patients who were hospitalized in the Unified Health System (SUS) because of the most severe clinical symptoms of Covid-19 suggest exactly the opposite.

In addition to not worsening the condition, asthma can play a protective role in infection with Sars-CoV-2, the virus that causes Covid-19. “Despite developing more clinical symptoms, patients with asthma were less likely to die from Covid-19 compared to individuals without asthma”, says one of the authors of the work, biologist and doctor of health sciences Fernando Augusto Lima Marson, from São Francisco University (USF), in Bragança Paulista (SP).

To reach this conclusion, the group formed by five researchers evaluated the clinical and demographic records of 1,129,838 patients hospitalized with Covid-19. Of this total, 43,245 (3.8%) were patients with asthma, a low prevalence that had already been pointed out by previous studies.

Among patients who required invasive ventilatory support, for example, 74.7% of patients with asthma died, while the percentage of deaths among patients without asthma was 78%. In the group receiving non-invasive ventilatory support, 20% of patients with asthma died versus 23.5% among patients without asthma.

Among those who did not require ventilatory support, 11.2% of patients with asthma died. The percentage of sick leave for patients without asthma in the same situation was 15.8%. All information was obtained from the OpenDataSUS database.

The researchers’ hypothesis is that the specifics of the immune response given by the body to asthma create an unfavorable scenario for the inflammatory escalation associated with the most severe form of Covid-19.

The person with asthma has a low production of inflammatory cytokines, a group of proteins that increases the body’s ability to destroy tumor cells, viruses and bacteria (interferons, for example). This stimulates an immune response mediated by defense cells (lymphocytes) TCD4+Th2, to the detriment of the Th1 subtype.

“The predominance of the Th2 response is beneficial because it can regulate and reduce the impact of the late phase of hyperinflammation, which is a critical point in severe respiratory infections”, explains Marson, who coordinates the Laboratory of Cellular and Molecular Biology at USF. He is also responsible for completion of course work at USF, where 100% of graduate students are full scholarship holders.

According to the research, which received funding from FAPESP (Foundation for Research Support of the State of São Paulo), asthma would cause further difficulties to Sars-CoV-2. Chronic inflammation of the lung alveoli of people with asthma decreases the amount of ACE-2 receptors (ACE-2, angiotensin-converting enzyme 2), a protein found on the surface of many cells in the body, including those of the epithelium of the respiratory system . It is used by the Covid-19 virus to penetrate inside cells, where it multiplies.

“The lower production of inflammatory cytokines and the lower amount of receptors for the virus result in less chance of serious infection”, says Marson. Larger amounts of eosinophils (white blood cells) present in the blood of people with asthma would also disfavor severe Covid-19.

For researchers, the impact of all these circumstances helps to understand why, although asthma affects 10% of the population, only 3.8% of patients diagnosed with Covid-19 and treated by SUS had the disease.

More research is needed

In Marson’s evaluation, the size of the evaluated sample makes a difference and can dilute some biases. “To give you an idea, at the same time that our study was carried out, a study in the United States that followed between 300 and 400 patients concluded that asthma was a risk factor”, she says.

He also states that the USF study may contain some misleading data because of the nature of the information analyzed. “Our study was based on data collected by a government agency. Although we have approached the real scenario in Brazil regarding the response of Covid-19 in relation to asthma, with the inclusion of many patients, the database still has limitations. There is, for example, no description of laboratory tests that could confirm the diagnosis of asthma”, says Marson.

New analysis and data collection will be carried out by the USF group starting this month, probably with a universe of 4 million people hospitalized after infection with Sars-CoV-2. “We are going to work with a more robust database and focus again on the outcome, but also on the influence of the vaccine against the virus”, adds the researcher.

The study published in the journal Frontiers in Medicine caused ramifications. A group of data scientists intends to verify the incidence rates of Covid-19 in people with asthma in nine municipalities in the region where the USF is located, in the interior of São Paulo.

From Portugal, came the invitation from the University of Lisbon for a partnership aimed at verifying the incidence of the infection in people with cystic fibrosis. “This disease causes physiological changes similar to those of asthma and a lot of mucus in the lungs, which could make it difficult for the virus to enter the cell”, observes Marson.