How Influenza Affects Asthma

If you have asthma, protecting yourself from influenza (The flu) is very important. Asthma and influenza are closely related because people with asthma are more susceptible to complications from influenza, and influenza can exacerbate asthma symptoms. 

People with asthma are among the high-risk groups for flu-related complications, with a higher rate of hospitalization for respiratory failure and severe asthma attacks during flu season.

How Influenza Causes Airway Inflammation

Influenza is a viral infection that primarily affects the respiratory system, leading to inflammation throughout the airways. This inflammation can cause various symptoms and complications, especially in individuals with pre-existing respiratory conditions like asthma or chronic obstructive pulmonary disease. 

The virus attaches to the cells using its surface proteins and enters them, leading to viral replication and cell damage. The body’s immune response is triggered to fight the influenza virus. White blood cells are recruited to the site of infection to eliminate the virus. This immune response, while essential for clearing the virus, also leads to the release of inflammatory cytokines and chemokines.

Inflammatory mediators such as interleukins and interferons are released in response to infection. These chemicals cause inflammation in the airways by increasing blood flow, leading to swelling and the recruitment of more immune cells to the site.

The replication of the influenza virus within epithelial cells results in cell death and shedding of the damaged cells into the airway. This cell damage and death further stimulate inflammation and lead to increased mucus production, which can clog the airways.

Inflammatory mediators cause the blood vessels in the airway walls to become more permeable, leading to leakage of fluid (edema) into the surrounding tissues. This swelling contributes to airway narrowing and difficulty in breathing.

Influenza infection stimulates goblet cells and submucosal glands in the respiratory tract to produce excessive mucus. The combination of increased mucus and inflammation can block airflow, causing symptoms like coughing and difficulty breathing.

The inflammation caused by influenza can also lead to bronchoconstriction (narrowing of the bronchi), particularly in individuals with reactive airway diseases such as asthma. The smooth muscles surrounding the airways can constrict due to inflammatory signals, leading to wheezing and shortness of breath.

Effects of Influenza on Respiratory Cilia

Influenza has a significant impact on the respiratory cilia, which are tiny hair-like structures that line the respiratory tract, playing a critical role in protecting the airways from infections and clearing mucus, debris, and pathogens. When the influenza virus infects the respiratory system, it can damage and impair the function of these cilia, leading to various complications.

The influenza virus causes cell death. This results in the loss or detachment of cilia from the epithelial surface, reducing the number of functioning ciliated cells. The influenza virus can cause ciliostasis, where the beating of the cilia is slowed or stopped. This damage affects the coordinated movement of cilia, which is essential for the mucociliary clearance mechanism.

When influenza impairs ciliary function or reduces the number of ciliated cells, the mucociliary clearance is severely compromised. This leads to the accumulation of mucus and debris in the airways, increasing the risk of secondary bacterial infections.

The release of various inflammatory mediators can further damage ciliated cells and exacerbate ciliary dysfunction by causing swelling and structural damage to the epithelial lining. The reduction in ciliary beat frequency diminishes the effectiveness of mucus clearance, allowing mucus and pathogens to accumulate in the lower airways.

Severe influenza infections can lead to the shedding or desquamation of the ciliated epithelium, leaving the underlying tissue exposed. This can result in more severe symptoms, such as persistent cough, and can prolong the recovery period.

Increased Susceptibility to Secondary Infections

With impaired mucociliary clearance, the respiratory tract becomes more vulnerable to bacterial superinfections. Bacteria that are normally expelled can now colonize the respiratory tract more easily, potentially leading to conditions like bacterial pneumonia, bronchitis, or sinusitis.

Triggering Asthma Attacks

The flu can act as a potent trigger for asthma attacks (also known as asthma exacerbations). The virus can irritate the lungs and airways, causing them to become even more swollen and inflamed. This leads to an increase in asthma symptoms such as wheezing, coughing, chest tightness, and shortness of breath.

Increased Mucus Production

Both asthma and influenza can significantly affect mucus production in the respiratory system. The combination of these conditions can lead to excessive mucus production, worsening respiratory symptoms, and increasing the risk of complications.

The mucus produced in asthma is often thick and sticky, making it more difficult to clear from the airways. This can lead to mucus plugging, where mucus becomes trapped in the smaller airways, further obstructing airflow and reducing oxygen exchange.

Inflammation in asthma can also damage the cilia. This leads to the buildup of mucus and contributes to prolonged coughing and respiratory discomfort.

Thus, both conditions promote excessive mucus production. In asthma, the mucus is already thick and sticky, and influenza further increases mucus viscosity and volume, making it even more difficult to clear from the airways. The combination of thick mucus, increased mucus production, and impaired mucociliary clearance can result in mucus plugging, where thick mucus blocks the small airways. This can cause severe airflow obstruction, reducing oxygen exchange and leading to low blood oxygen levels.

Complications like Pneumonia

People with asthma are at a higher risk of developing complications from influenza, such as pneumonia (a lung infection), which can be more severe and harder to treat in those with pre-existing respiratory conditions.

Heightened Immune Response

The body's immune response to influenza in asthmatic individuals may lead to an overproduction of inflammatory chemicals like histamines and leukotrienes. These chemicals can cause the muscles around the airways to tighten, making the airways even narrower and worsening asthma symptoms.

Reduced Lung Function

Influenza can cause a temporary reduction in lung function, which can be more problematic for people with asthma. This reduction makes it more difficult for them to manage their regular asthma symptoms and can lead to prolonged recovery times.

Prevention Tips 

Getting the influenza vaccine every year is one of the most effective ways for asthmatic patients to reduce the risk of severe influenza and associated hospitalizations. The vaccine helps reduce the risk of catching influenza and the severity of illness if infected. Make it a family affair. Vaccinate the whole family to protect family members who have asthma.

People with asthma should have an updated asthma action plan, which includes steps to take during respiratory infections, and ensure they have access to rescue medications.

Frequent hand washing, avoiding close contact with people who are sick, and covering the mouth and nose when coughing or sneezing can help reduce the risk of catching the flu.

Early treatment with antiviral medications can help reduce the severity and duration of influenza symptoms, lowering the risk of severe asthma exacerbations.

Use controller medications as prescribed to keep asthma well-managed and reduce the risk of complications from the flu.