Seasonal influenza, COVID-19, and the common cold are three distinct respiratory illnesses caused by completely different viral agents. However, the similarity in initial clinical symptoms such as fever, cough, sore throat, fatigue, and runny nose often makes it difficult to differentiate them, causing confusion and delay in applying appropriate treatment measures.

Understanding the differences between these three conditions is the first step to protecting your health. In parallel, the fundamental role of nutrition in building and maintaining a healthy immune system – the body’s most important natural defense against these pathogens – will also be clarified and emphasized.

1.  Overview of common respiratory diseases: Seasonal flu, COVID-19, colds

Seasonal flu, colds, and COVID-19 are all acute respiratory infections caused by viruses

Acute respiratory infections such as seasonal influenza, COVID-19, and the common cold are global health concerns. Seasonal influenza causes a significant burden of hundreds of thousands of deaths worldwide each year [1]. Colds are the most common infection, especially in children [2], while the COVID-19 pandemic has caused millions of deaths since its emergence [3].

In essence, seasonal flu is caused by Influenza viruses (mainly types A and B), which are characterized by their ability to continuously mutate antigens, requiring annual vaccine updates. COVID-19, caused by the SARS-CoV-2 virus, is highly contagious and has a wide spectrum of disease, ranging from mild to severe, especially in high-risk groups. The common cold, caused by many viruses (most commonly Rhinovirus), is usually mild and self-limiting.

Although the initial symptoms are similar, it is essential to accurately distinguish these three conditions. It helps to correctly assess the risk of potential complications, thereby making effective treatment choices. At the same time, correctly identifying the disease is also the basis for applying infection prevention measures such as appropriate isolation time, contributing to the best protection of personal and community health.

2. Clinical manifestations of seasonal flu, COVID-19 and colds

Distinguishing based solely on symptoms can be difficult, especially in the early stages. However, there are differences to note:

Similar symptoms

Cough, fever, sore throat, etc. are typical symptoms of seasonal flu, cold and COVID-19

•     Cough
•     Sore throat
•     Runny or stuffy nose
•     Body aches or muscle aches
•     Headache
•     Fatigue

Differences

Although there are similarities, the severity, duration and progression of symptoms of colds, flu and COVID-19 are different. Specifically:

The differences in symptoms of seasonal flu, colds and COVID-19[4]

3. Nutrition – the ultimate shield for a healthy immune system

The immune system is a complex network of cells, tissues, and organs that work together to protect the body from pathogens such as viruses and bacteria. Nutrition plays a vital role in building, maintaining, and optimizing the function of the immune system. A nutritionally deficient diet can weaken the body’s defenses, increase susceptibility to infection, and prolong recovery time[5].

The role of nutrition on the immune system

Nutrition – Shield to protect the immune system

Nutrition provides core ingredients such as amino acids from proteins or essential fatty acids, which are considered “building materials” for the body to synthesize important immune components such as antibodies, cytokines and immune cells themselves. The role of nutrition goes beyond that, as it is directly involved in regulating complex inflammatory and immune responses, ensuring the system operates in balance and efficiency. Specifically, essential nutrients such as proteins, vitamins and minerals provide raw materials for the production, proliferation and maintenance of effective immune cells (such as T cells, B cells, macrophages) and important molecules such as antibodies. Many micronutrients, such as Zinc, Selenium, Vitamins C and D, act as co-factors for enzymes or as molecular “switches” that directly regulate the function of immune cells, allowing to control the intensity and duration of inflammatory responses. In addition, nutrients such as Omega-3 fatty acids and antioxidants (Vitamins E, C) protect immune cell membranes from damage caused by oxidative stress during the fight against pathogens, while also participating in regulating the production of inflammatory mediators. Nutrition also affects the immune system by nurturing a healthy gut microbiome, which trains and balances the majority of the body’s immune responses [6].

Golden nutrients boost the immune system

•     Protein

○      How it works: A major constituent of immune cells (lymphocytes, macrophages), antibodies (immunoglobulins) and signaling molecules (cytokines). Protein deficiency reduces antibody production and impairs immune cell function.

○      Sources of food: Poultry, fish, eggs, milk and milk products, legumes (soybeans, chickpeas, lentils), nuts, whole grains.

•   Antioxidants System: Protects immune cells from oxidative stress – cell damage caused by free radicals, which increases during the fight against infection. Antioxidants are made up of the following 4 vitamins and minerals:

○      Vitamin C: Enhances the function of white blood cells, promotes the production of interferon – a natural antiviral substance. Vitamin C is abundant in guava, oranges, tangerines, kiwi, strawberries, bell peppers, broccoli.

○      Vitamin E: Plays a role in protecting immune cell membranes from oxidative damage, found in vegetable oils such as sunflower oil, nuts such as almonds, walnuts, sunflower seeds and dark green leafy vegetables..

○      Vitamin A: Important for the growth and differentiation of immune cells, and for maintaining the integrity of the respiratory and digestive tract mucosa. Vitamin A is found in abundance in liver, egg yolks, milk, carrots, sweet potatoes, pumpkin, spinach, and kale.

○      Selenium: A component of antioxidant enzymes, necessary for optimal immune cell function. Selenium is abundant in seafood (tuna, sardines, shrimp), poultry, eggs, nuts (especially Sachi seeds).

•     Omega-3 (EPA & DHA): This polyunsaturated fatty acid has anti-inflammatory properties, allowing to regulate the immune response, avoiding excessive inflammation that is harmful to the body. Natural sources of Omega 3 supplements often come from fatty fish (salmon, mackerel, herring, sardines), fish oil, flaxseeds, chia seeds, walnuts.
•     Probiotics: About 70 – 80% of immune cells are located in the intestine[7]. Therefore, a healthy intestinal microflora plays an important role in “training” and regulating the immune system. Probiotics balance the microflora, strengthen the intestinal mucosal barrier and regulate immunity. In nature, probiotics are often found in foods such as: Yogurt, kefir, sauerkraut, kimchi, tempeh, kombucha.
•     Colostrum: It is milk produced in the first few days after birth and is rich in antibodies (especially Immunoglobulin G – IgG), growth factors, and other immune components, providing passive immunity and supporting the development of the immature immune system in newborns. Supplements containing IgG from bovine colostrum have also been studied for their immune-supporting properties.

To meet specific nutritional needs and support the strengthening of the immune shield, especially during sensitive periods or when the body needs to recover, nutritional solutions are essential. Researched and developed by Nutricare and the Nutricare Medical Nutrition Institute – USA (NMNI-USA), ColosCare 24h is optimally designed for children and ColosCare Adult supports health improvement for the elderly. For young children, building a solid immune foundation is extremely important. ColosCare 24h meets this need with a breakthrough formula, rich in high-quality IgG antibodies (1200+) from 24-hour colostrum imported from the US, providing effective resistance enhancement, reducing the rate of respiratory infections of the product that has been clinically proven. At the same time, advanced Postbiotic technology with 10 billion probiotics, HMO and fiber not only supports healthy digestion, prevents constipation but also plays an important role in balancing the intestinal immune system. The product also supplements easily absorbed protein, Calcium, Vitamin D3 and 56 essential nutrients, creating momentum for children to gain weight and develop comprehensively.

Not only children, the elderly also need a healthy immune system. ColosCare Adult is specially designed with natural IgG antibodies from imported colostrum from the US, combined with Lactoferrin and probiotics, forming a trio to effectively strengthen the immune system. The product also supplements high energy, rich in protein, calcium and vitamin D3, allowing to maintain and strengthen the health of the musculoskeletal system, bones and joints. In particular, the formula does not contain lactose, supplemented with 100% soluble fiber (Polydextrose) to help the digestive system function well, reduce constipation, create optimal conditions for nutrient absorption to support the body’s overall resistance.

Principles of building a nutritional diet to strengthen immunity

To strengthen and establish the immune system, the diet requires the following 5 basic principles:

•     Adequate energy and balanced nutrition: Ensure adequate calories, protein, healthy fats and complex carbohydrates.
•     Diversity of foods: Eat a variety of fruits and vegetables of different colors to get enough vitamins, minerals and antioxidants.
•     Prioritize fresh, seasonal foods: Fresh foods often retain more nutrients.
•     Sufficient water: Water is necessary for all body functions, including immune function and maintaining respiratory mucosal moisture.
•     Limit processed foods, refined sugars, saturated fats and trans fats, which can cause inflammation and negatively affect the immune system.

4. Other preventive and supportive measures

In addition to nutrition, the following preventive and supportive measures are also extremely important:

Personal hygiene

Hand washing is an effective way to prevent flu

Personal hygiene measures play a fundamental role in interrupting the transmission of respiratory viruses. Frequent handwashing with soap and water for at least 20 seconds, or alternatively using an alcohol-based hand sanitizer (at least 60% alcohol content), is a core action that has been proven effective in removing or inactivating pathogens on hands[8]. Hands are a common means of introducing viruses into the body through the mucous membranes of the eyes, nose, and mouth, hence avoiding touching the face with unwashed hands is an important step in preventing self-infection.

In particular, regular cleaning and disinfection of frequently touched surfaces such as door handles, light switches, telephones, and keyboards cannot be overlooked, as the virus can survive on objects for a certain period of time and become an indirect source of infection when touched and then brought to the face[9].

Healthy lifestyle

In addition to hygiene measures, maintaining a healthy lifestyle plays an essential role in strengthening the body’s natural defenses. Sufficient and quality sleep (7-9 hours per night is recommended for adults) is fundamental for optimal immune function, as many important immune activities occur during sleep[10].

In parallel, regular physical activity, aiming for at least 300 minutes of moderate intensity per week, not only improves overall health but can also enhance immune response and reduce inflammation[11]. Effective stress management through methods such as meditation, yoga, or spending time on hobbies is also important, as chronic stress has been shown to weaken the immune system.

Finally, avoiding cigarette smoke and limiting alcohol consumption are essential, as both of these factors damage the respiratory system and reduce the body’s ability to fight infection[12].

Vaccination

In the arsenal of antiviral respiratory disease prevention, vaccination is a proactive and highly effective strategy. Annual seasonal influenza vaccination is widely recommended as the most effective method to reduce the risk of influenza and its serious complications, it’s especially important as influenza viruses change frequently[13].

Similarly, completing the COVID-19 vaccination schedule as recommended by health authorities plays a key role in significantly reducing the risk of severe disease, hospitalization, and death from SARS-CoV-2, even as new variants emerge[14]. Both vaccines work by “training” the immune system to recognize and fight the virus more effectively when exposed to it.

5. When is it necessary to see a doctor?

Although many cases of colds, flu, and mild COVID-19 can be resolved at home, it is important to recognize warning signs that require medical intervention.

Warning signs to seek immediate medical attention

Regularly monitor for signs of illness and visit medical facilities promptly

•     Difficulty breathing or feeling short of breath.
•     Persistent chest pain or pressure.
•     High fever that does not go down after taking fever-reducing medicine or fever that keeps coming back.
•     Skin, lips or fingernails turning blue or gray.
•     In children: rapid breathing or difficulty breathing, blue lips or face, chest pain, severe muscle pain, dehydration (no urination for 8 hours, dry mouth, no tears when crying), seizures, fever over 40°C, fever or cough that improves and then gets worse.

Especially for high-risk groups (people over 65 years old, people with underlying diseases such as cardiovascular disease, diabetes, chronic lung disease, immunodeficiency, obesity, children under 5 years old, pregnant women), early examination upon suspected symptoms detected allows to diagnose accurately, assess the severity and have timely treatment plans, minimizing the risk of complications.

Conclusion

Distinguishing between seasonal flu, COVID-19 and the common cold can sometimes be a challenge due to the similarity in symptoms. However, by carefully observing the speed of onset, systemic symptoms, characteristic respiratory manifestations and severity, we can make a more accurate initial assessment. The most important thing is not to be subjective, always closely monitor symptoms and seek timely medical attention when there are warning signs or when uncertain about the condition. Correct understanding of each disease enables right actions to protect the health of ourselves and our families.