Protect Yourself Against The Flu and RSV With Essential Vitamins

Influenza, the common cold, respiratory syncytial virus (RSV) and COVID-19 are respiratory infections caused by different viruses. Although these illnesses can circulate at the same time and cause overlapping symptoms, they may differ in their typical onset, severity and risk of complications. Respiratory virus activity often increases during fall and winter in temperate regions, but the timing and intensity of each virus can vary from season to season.¹

Norovirus also commonly causes outbreaks during the colder months, but it is not a respiratory virus. It affects the stomach and intestines and causes acute gastroenteritis.²

The common cold can be caused by several viruses, including rhinoviruses, seasonal coronaviruses and parainfluenza viruses. Cold symptoms are generally milder than flu symptoms and are more likely to include a runny or stuffy nose, sneezing, sore throat and cough.³

Influenza, or the flu, is caused specifically by influenza viruses. Symptoms often begin more abruptly and may include fever or chills, cough, sore throat, headache, pronounced fatigue and muscle or body aches. However, not everyone with influenza develops a fever.

Unlike most common colds, influenza can cause serious complications, including pneumonia. Young children, adults aged 65 years and older, pregnant people and individuals with certain chronic medical conditions or weakened immune systems have a higher risk of severe illness.⁴

Because colds, influenza, RSV and COVID-19 share many symptoms, it may be difficult and sometimes impossible to distinguish between them based on symptoms alone. Testing may be appropriate when the result could guide treatment or other precautions, particularly when symptoms are severe or the affected person has a higher risk of complications.

Respiratory syncytial virus, commonly called RSV, is a contagious respiratory virus that infects the nose, throat, airways and lungs. It usually causes mild, cold-like symptoms, but its symptoms are not specific enough to reliably distinguish it from a cold, influenza or COVID-19 based on symptoms alone.⁵

RSV symptoms may include a runny nose, decreased appetite, cough, sneezing, fever and wheezing. Most infections improve on their own within one or two weeks. In very young infants, symptoms can be less typical and may include irritability, reduced activity, difficulty feeding or pauses in breathing.

RSV can cause serious lower respiratory tract illness, including bronchiolitis and pneumonia. Infants — particularly those younger than six months —  older adults and people with certain underlying medical conditions are among those at increased risk of severe RSV illness and hospitalization.

Norovirus is not a respiratory virus and does not cause influenza. It is a highly contagious gastrointestinal virus that causes inflammation of the stomach or intestines. The most common symptoms are sudden vomiting, diarrhea, nausea and stomach pain.

Norovirus illness is sometimes called the “stomach flu,” but this term is misleading because norovirus is unrelated to influenza. The seasonal flu vaccine does not protect against norovirus, the common cold, RSV or COVID-19. Each of these infections is caused by a different virus and requires its own prevention approach.

Influenza, RSV, COVID-19 and the viruses that cause the common cold can produce many of the same symptoms. Cough, sore throat, nasal congestion, fatigue, fever and body aches may occur with more than one infection. The severity and combination of symptoms can vary according to age, immune status, underlying health conditions and the particular virus involved. Although certain symptom patterns may suggest one illness over another, symptoms alone cannot reliably identify which virus is responsible.

Flu symptoms typically begin suddenly and may be more intense than symptoms of the common cold.

Common symptoms include:

• Fever or feeling feverish and chills
• Cough
• Sore throat
• Runny or stuffy nose
• Muscle or body aches
• Headache
• Fatigue

Some people, particularly children may also experience vomiting or diarrhea. However, influenza is primarily a respiratory illness, and not everyone with flu develops a fever.⁶

RSV often begins with mild, cold-like symptoms that may appear in stages rather than all at once.

Common symptoms include:

• Runny nose
• Reduced appetite
• Cough
• Sneezing
• Fever
• Wheezing

Infants may show irritability, reduced activity, difficulty feeding or pauses in breathing instead of the symptoms more commonly seen in older children and adults. Severe RSV can cause bronchiolitis or pneumonia and may lead to difficulty breathing.⁷

COVID-19 may cause fever or chills, cough, sore throat, nasal congestion, fatigue, headache, body aches, shortness of breath, nausea, vomiting or diarrhea. Because many of these symptoms also occur with influenza and other respiratory infections, testing may help to distinguish COVID-19 from flu.⁸

Common colds are more likely to cause a runny or stuffy nose, sneezing, sore throat and cough. Headache, mild body aches and fever can also occur, but cold symptoms are generally milder than flu symptoms.⁹

People at increased risk of severe respiratory illness should contact a healthcare professional promptly if they develop symptoms. Antiviral treatment for influenza or COVID-19 is most effective when started early and may reduce the risk of severe illness in eligible patients.

• Seek urgent medical care for warning signs such as:
• Difficulty breathing or shortness of breath
• Persistent chest pain or pressure
• Confusion, severe dizziness or difficulty waking
• Bluish, pale or gray lips, skin or nail beds
• Signs of dehydration, such as very little urination
• Seizures
• Severe weakness or unsteadiness
• Fever or cough that improves but then returns or worsens

In infants and children, fast breathing, ribs pulling inward with each breath, poor fluid intake or reduced alertness also requires prompt medical attention. Any fever of 100.4°F (38°C) or higher in an infant younger than 12 weeks requires immediate medical care.

Respiratory viruses do not all peak at the same time. In the United States, influenza and RSV generally increase during fall and winter, whereas COVID-19 can produce waves at different times of the year. Rhinoviruses, which cause many common colds, often increase when children return to school.¹⁰

The overall level of acute respiratory illness prompting healthcare visits in the United States remains low. However, seasonal influenza activity is increasing across parts of the country, with early-season activity particularly evident on the West Coast. COVID-19 activity has been declining nationally but remains elevated in some regions, while RSV activity continues to be very low in most areas. Rhinovirus/enterovirus activity also remains elevated nationally.

These evolving trends highlight the importance of continued surveillance as the fall and winter respiratory virus season progresses.

Several interacting factors help explain why respiratory infections often increase during fall and winter:

As temperatures fall, people spend more time together in enclosed spaces. Respiratory viruses can spread through the air, particularly in crowded or poorly ventilated indoor environments. Opening windows when practical, improving ventilation and using appropriate air filtration can reduce the concentration of virus-containing particles indoors.¹¹

The beginning of the school year brings children and families back into close contact, creating more opportunities for respiratory viruses to spread through schools, households and communities. Increases in rhinovirus infections are frequently observed around school reopening, although school attendance is only one of several contributing factors. Workplaces and other shared indoor environments may similarly facilitate transmission when people spend extended periods in close contact.¹²

Temperature and humidity can affect both respiratory viruses and the body’s defenses against them. Influenza and several other respiratory viruses transmit more efficiently under certain cool, dry conditions. Dry air may also impair mucus clearance and other protective responses in the respiratory tract, although findings from laboratory and animal studies do not explain every aspect of seasonal transmission in people.^13,14

Protection from previous infections or vaccination can decrease over time, while circulating viruses continue to change. Waning protection may leave more people susceptible to infection, particularly when circulating influenza strains or SARS-CoV-2 variants differ from those encountered previously. Vaccination and other recommended immunizations can help reduce the risk of severe illness from influenza, COVID-19 and RSV in eligible groups.

Influenza, RSV, COVID-19 and cold-causing viruses can circulate during the same period, but their peaks may occur at different times. When their waves overlap, more people may become ill and healthcare systems may experience increased pressure. This is particularly important for infants, older adults, pregnant people, individuals with weakened immune systems and those with chronic heart, lung, kidney or metabolic conditions. Fall is therefore an important time to review recommended vaccinations and immunizations, improve indoor air quality and make a plan for testing or early medical care if symptoms develop. Because local virus activity can differ from national patterns, current public health surveillance provides a more accurate picture than assuming every cough or fever is caused by flu.

No single precaution can prevent every respiratory infection. The best protection against flu and other respiratory viruses comes from combining vaccination, cleaner air, good hygiene, appropriate mask use and healthy habits that support normal immune function.

Annual influenza vaccination is the most effective way to reduce the risk of flu and its potentially serious complications. Although some vaccinated people may still develop influenza, vaccination can reduce the likelihood of illness, hospitalization and death and may make the illness less severe if infection occurs.¹⁵

The flu shot protects against the influenza viruses expected to circulate during a particular flu season. In the United States, all vaccines for the 2026–2027 season are trivalent and are designed to protect against:

• Influenza A(H1N1)
• Influenza A(H3N2)
• Influenza B/Victoria

Therefore, the flu shot can protect against both influenza A and influenza B viruses included in that season’s vaccine. However, protection varies depending on a person’s age and health and how closely the vaccine viruses match the viruses that circulate.

The flu shot does not protect against:

• The viruses that cause the common cold
• RSV
• COVID-19
• Norovirus
• Other causes of respiratory or gastrointestinal illness

Separate vaccines or immunizations are available for COVID-19 and for certain people at increased risk from RSV. A healthcare professional can advise which immunizations are appropriate based on age, pregnancy, health history and current recommendations.

Protection from the flu vaccine takes approximately two weeks to develop. In the United States, September and October are generally appropriate times for most people to receive the vaccine, ideally before influenza begins spreading widely.

Yes. Wearing a mask can help reduce the spread of influenza and other respiratory viruses. A mask worn by an infected person can reduce the number of infectious particles released into the surrounding air, while a mask worn by an uninfected person can reduce the number of particles inhaled.¹⁶

Protection depends on the mask’s filtration and fit. Surgical or disposable masks can provide some protection against flu, particularly when they fit closely over the nose and mouth. Well-fitting respirators such as N95 or KN95 masks generally provide greater protection to the wearer because they filter particles more effectively and allow less air to leak around the edges.¹⁶

Masking may be especially helpful:

• In crowded indoor spaces
• When respiratory-virus activity is increasing
• After a recent exposure
• When you are sick or recovering
• When you or someone around you has a higher risk of severe illness

Masks provide an additional layer of protection rather than a guarantee against infection.

Respiratory viruses can accumulate in crowded or poorly ventilated indoor spaces. Bringing in outdoor air, opening windows when practical, using exhaust fans and properly operating heating, ventilation and air-conditioning systems can help reduce exposure. Portable high-efficiency particulate air (HEPA) filtration may provide an additional layer of protection in appropriate indoor settings.

Respiratory viruses can accumulate in crowded or poorly ventilated indoor spaces. Bringing in outdoor air, opening windows when practical, using exhaust fans and properly operating heating, ventilation and air-conditioning systems can help reduce exposure. Portable high-efficiency particulate air (HEPA) filtration may provide an additional layer of protection in appropriate indoor settings.

Simple hygiene practices remain an important part of respiratory virus prevention:

• Wash your hands regularly with soap and water.
• Cover coughs and sneezes with a tissue or your elbow.
• Avoid touching your eyes, nose and mouth with unwashed hands.
• Clean frequently touched surfaces when someone is ill.
• Avoid close contact with people who are sick when possible.
• Stay home and away from others when you are ill.

Handwashing with soap and water is particularly important for preventing norovirus. Unlike respiratory viruses, norovirus commonly spreads through contaminated hands, food, liquids and surfaces. Alcohol-based hand sanitizer alone does not work well against norovirus.

People often search for vitamins to boost the immune system, but “support” is more scientifically accurate than “boost.” The immune system depends on adequate nutrition, sleep, physical activity and many other factors. No food, vitamin or dietary supplement can guarantee protection against influenza, RSV, COVID-19 or the common cold.

Helpful everyday habits include:

• Eating a varied, nutrient-rich diet
• Getting adequate and consistent sleep
• Participating in regular physical activity
• Managing chronic health conditions
• Avoiding smoking and exposure to tobacco smoke
• Limiting alcohol intake
• Correcting confirmed nutrient deficiencies with professional guidance

These measures support overall health and normal immune function, but they do not replace vaccination or other evidence-based precautions.¹⁷

Several nutrients contribute to the normal development and activity of immune cells. These include vitamins A, C, D, E, B6, B12 and folate, along with minerals such as zinc, selenium, iron and copper.17 A balanced diet can provide many of these nutrients, while supplementation may be appropriate when dietary intake is inadequate, a deficiency is present or a healthcare professional identifies an increased need.

Taking more than the body needs does not necessarily provide greater protection. High doses of some nutrients can cause adverse effects or interact with medications. Supplements should complement, not replace a nutritious diet, vaccination or appropriate medical care.

Vitamin C contributes to normal immune function, but it does not reliably prevent colds in the general population. Research suggests that taking vitamin C regularly may modestly shorten the duration of a cold and reduce symptom severity. However, beginning vitamin C only after cold symptoms appear has not consistently provided the same benefit.^18,19

Evidence that vitamin C prevents or treats influenza or RSV is insufficient. Claims that vitamin C or combinations marketed as “vitamins for colds” or “vitamins to prevent RSV” can replace vaccination, testing or medical treatment are not supported by current evidence.

Vitamin D is important for immune function, and correcting vitamin D deficiency is beneficial for overall health. However, recent meta-analyses have not shown that vitamin D supplementation consistently prevents acute respiratory infections in the general population.²⁰ Vitamin D should therefore be taken according to individual nutritional needs rather than as a guaranteed way to prevent flu or RSV.

For people seeking the best vitamins to protect against flu, the most appropriate approach is to meet established nutrient requirements and correct deficiencies. Vitamins support normal immune function, but vaccination and layered preventive measures provide more direct protection against respiratory viruses.