Flu in Adults

Flu in Adults Facts

  • Influenza (flu) is an acute viral infection of the nose, throat, and lungs. It is a common cause of acute respiratory illness and can affect people of all ages.
  • It occurs every year beginning in late fall, with the peak season for the flu in the northern hemisphere extending from November through March.
  • It infects in a widespread fashion, affecting people of different ages at the same time.
  • Although influenza is one of many viruses circulating during the season, it is an important cause of illness and hospitalization. Up to 80% of people who are hospitalized due to the flu have conditions that put them at risk of severe infection or even death.
  • The flu is also associated with an increased occurrence of heart attacks and strokes.
  • While most people are aware that older or chronically ill people are at risk for serious complications of flu, groups such as pregnant women, young children, and obese people are also at high risk.

Some also confuse influenza with the term stomach flu. However, the latter is an illness associated with nausea, vomiting, and diarrhea and can be caused by bacteria and viruses but not the influenza viruses. It is a stomach illness, whereas the flu is an illness of the respiratory system.

What Causes Flu in Adults?

Three types of influenza viruses exist. Types A and B cause epidemics of severe respiratory illnesses known as "the flu," and type C causes a mild illness not associated with epidemics. Type A is divided into different subtypes based on the chemical structure of the virus. The H1N1 swine flu virus is a type A influenza virus. Type B is not divided into subtypes. Both type A and type B are responsible for the seasonal influenza outbreaks.

  • Outbreaks occur more frequently in the winter months. Many factors may play a role in this seasonal pattern:
    • The virus survives for longer periods indoors in winter because the relative humidity of indoor air is very low in comparison to the outside air.
    • The virus is in droplets that are coughed or sneezed; it infects others by being inhaled or by landing on sensitive body areas such as the eyes, nose, or mouth. These droplets generally travel no further than 6 feet.
    • In the winter, humans tend to be indoors more and thus have closer contact with each other, which makes it easier for the virus to spread.
  • Flu outbreaks are classified as epidemics (occurring in a set geographical area) or pandemics (a worldwide occurrence). A flu pandemic can occur when a new influenza A virus emerges against which there is very little immunity already in the human population. Because there is little immunity, the new virus can spread from person to person very easily and can sicken more people. In 2009, a pandemic influenza strain began circulating called "novel" H1N1 influenza or swine flu.
  • Influenza is a contagious disease. The virus is spread when you either inhale infected droplets in the air (spread when an infected person coughs or sneezes) or when you come in direct contact with an infected person's secretions (for example, by kissing, sharing of handkerchiefs and other items, and through use of objects such as spoons and forks). Touching surfaces, such as doorknobs, elevator buttons, keyboards, and phones, are other ways to transfer the virus to your hands, which may then contact the nose, mouth, or eyes, where the virus gets absorbed.
  • A sudden increase in the number of school-aged children sick at home with flu-like illness may indicate the arrival of flu season. This outbreak is soon followed by similar infection in other age groups, especially among adults.

Flu Vaccine Side Effects

In general, all medications, including intramuscular, intradermal, and nasal-spray vaccines, have side effects and the potential for allergic reactions. For most medicines and vaccines, the side effects or reactions are infrequent and are minimal if they do occur. Consequently, the pros far outweigh the cons for vaccination.

What Are Symptoms and Signs of Flu in Adults?

Flu symptoms and signs usually come on suddenly.

  • Fever (usually high)
  • Severe aches and pains in the joints and muscles (especially in the back) and around the eyes
  • Generalized weakness
  • Ill appearance with warm, flushed skin and red, watery eyes
  • Headache
  • Dry cough
  • Sore throat and watery discharge from the nose or nasal congestion
  • Vomiting or diarrhea is sometimes seen, particularly in children

What Is the Incubation Period for Flu in Adults?

The incubation period is the time between exposure to the virus and symptoms of illness. The incubation period for the flu is from two to four days.

Flu vs. Cold

Many people commonly and incorrectly confuse influenza (the flu) with the common cold. The common cold is a mild infection frequently caused by viruses other than the influenza virus.

Differentiating a cold from the flu by symptoms alone can sometimes be difficult or impossible, but in general, people with the flu get sick more suddenly, look much sicker, and feel much weaker than if the ailment were a common cold. Higher fever, body aches, extreme tiredness, and dry cough are more often symptoms of the flu, whereas runny or stuffy nose are more often associated with common colds.

When Should Adults With the Flu Call a Doctor?

Most people with the flu take care of themselves at home and do not seek medical care.

Quite a few groups of people are at high risk for developing complications of the flu (of course, anyone can develop serious complications and may be unaware of being at high risk). Groups at high risk include the following:
  • Those with chronic diseases of the heart, lungs, liver, blood, or kidneys (any condition that affects a major organ system)
  • Smokers
  • Pregnant women
  • People with obesity (body mass index or BMI over 40)
  • People with diabetes
  • People with disorders of the brain, spinal cord, peripheral nerves, or muscles (examples include cerebral palsy, seizures, intellectual disability, stroke, and spinal cord injury)
  • People with weak immune systems due to disease or medication (such as people with HIV infection, or who are on chronic steroids or tumor necrosis alpha inhibitor drugs)
  • People with cancer, including cancer survivors
  • People with disorders of metabolism or mitochondria
  • Residents of nursing homes and other facilities
  • People older than 65 years of age
  • People on long-term aspirin therapy
  • People who provide care to those at high risk for complications of flu, such as home caregivers, preschool workers, or health care workers

People in a high-risk group should receive the flu vaccine and pneumococcal vaccines before the start of flu season. Pneumococcus is one of the most common causes of bacterial pneumonia that is preventable by vaccine. They should be especially aware of when to see a doctor or go to the hospital. People at high risk may benefit from early treatment with antiviral drugs that combat the influenza virus. You should contact your doctor or seek care in a hospital's emergency department for the following symptoms, which may be a sign of complications:

  • Dehydration and unable to drink fluids
  • Bloody or brown sputum (saliva mixed with mucus and coughed up)
  • Difficulty breathing
  • Turning blue (a sign of poor oxygenation)
  • Worsening fever
  • Return of fever, cough, and other symptoms in the second week after the onset of the flu or worsening after symptoms have begun to improve

These symptoms and signs may signify a more severe and complicated attack of flu (most importantly, the development of pneumonia). Pneumonia is an infection of the lungs, and it may be caused by the flu virus itself or by a bacterial infection that may occur when the person is weakened during a flu attack.

What Is the Duration of Flu in Adults?

The illness from uncomplicated flu lasts from three to seven days in most adults. Cough and malaise (feeling tired or weak) can last up to two weeks following illness. Complications such as pneumonia can occur in some cases, which causes a more prolonged illness.

What Is the Contagious Period for Flu in Adults?

  • A person with flu is contagious for up to seven days after the onset of the illness, although the virus can be detected in the secretions up to 24 hours before the onset of symptoms. Thus, an individual can transmit the virus one day before symptoms begin.
  • In young children, the virus can still be spread in body secretions into the second week of illness.
  • To avoid spreading the illness, the U.S. Centers for Disease Control and Prevention (CDC) recommends that people stay home until 24 hours after the fever is gone without using fever reducers, except to obtain necessities or to seek medical care.

How Do Health Care Professionals Diagnose Flu in Adults?

In most cases, diagnosis of the flu is determined by the symptoms, especially when these occur during the peak flu season. Sometimes, the doctor may need to perform special tests to be sure the influenza virus is responsible for the symptoms and not one of the many other viruses that circulate at the same time. If an influenza virus test is positive, medication may be helpful.

A sample is taken from the back of the throat or nose. To take a sample, the doctor uses a long sterile swab and rubs the tip at the back of the throat or inside the nose. The swab is sealed in a packet for transporting specimens and sent to a lab. Some offices may use a rapid test that can be performed in the office with the result available in 30 minutes. Some rapid tests detect only influenza A virus, while others can detect both influenza A and influenza B. Some cases of the flu may be missed by the rapid tests.

What Is the Treatment for Flu in Adults?

Treatments for flu (influenza) include home remedies such as resting in bed, avoiding physical exertion, and avoiding alcohol and tobacco use. Hydration is important, and minor aches and pains can be relived with over-the-counter (OTC) medication such as acetaminophen (Tylenol), ibuprofen (Advil), and naproxen (Aleve). Avoid spreading germs and the flu virus by washing hands often or using alcohol-based hand sanitizers. Stay away from others until you are fever free for 24 hours. Cover sneezes or coughs with the inside of your elbow, or use a tissue and throw it away promptly.

Medical treatment for the flu include medications (antiviral drugs) prescribed to decrease the severity and duration of the infection. These drugs include the class known as neuraminidase inhibitors such as oseltamivir (Tamiflu).

To avoid resistance to antibiotics when they are truly needed, antibiotics are only prescribed when there is evidence of a bacterial infection, such as pneumonia. Antibiotics do not treat viral infections such as the flu, and they do not prevent bacterial infections that may occur because of the flu.

What Are Home Remedies for Flu in Adults?

  • Rest in bed. Avoid physical exertion. Avoid using alcohol and tobacco.
  • Drink plenty of fluids such as water, fruit juices, and clear soups (like chicken soup). Water should never be the sole or main liquid consumed because it does not contain adequate electrolytes (sodium and potassium, for example) that the body requires. Commercially available products such as Gatorade and other similar sports drinks can be useful in this regard. For children, ORS (oral rehydration solution) packets are another good way to replenish the body. A similar rehydrating solution can be made at home using salt, sugar, and plain or rice water. Adding some orange juice and mashed bananas enhances the taste and also provides a good source of potassium. Such a solution can be used by anyone, regardless of age.
  • Treat fever and aches with over-the-counter medications such as acetaminophen (Tylenol), ibuprofen (Advil or Motrin), and naproxen (Aleve or Naprosyn).
    • Caution: For children younger than 16 years of age with symptoms of flu or cold, aspirin should not be used because of its association with Reye's syndrome, which can cause liver and brain damage.
  • Use cough suppressants and expectorants to treat the cough.
  • Cough and sneeze into a soft tissue or handkerchief. Carefully dispose of tissues after using them.
  • Stay away from who are well until you have not had fever for 24 hours.

What Foods Should You Eat When You Have the Flu?

  • Although no particular foods have been shown to decrease the length of the illness, it is recommended to drink plenty of fluids, including water and juices to avoid dehydration, and eat food even though the appetite may be decreased.
  • Eat foods with protein, such as meats, beans, and nuts and those that may soothe, such as warm soup or cold juice pops.

What Medications Treat Flu in Adults?

Some medications can be used to decrease the severity and duration of a flu attack. These are referred to as antiviral drugs. Antiviral medications are often given to those who are very sick, such as those in the hospital and others who are at higher risk of complications.

  • Zanamivir (Relenza), oseltamivir (Tamiflu), and peramivir (Rapivab) are neuraminidase inhibitor drugs recommended to treat seasonal flu. They are active against both influenza A and B although resistance to these drugs may develop in some strains of influenza A.
    • Zanamivir and oseltamivir are most effective when given within 48 hours of the onset of illness. They can decrease the duration of the disease by one day if used within this early time period. They may also be able to reduce the incidence of complications from the flu. The drugs are usually given for a period of about five to seven days.
    • These antiviral drugs are safe for children and pregnant women.
    • Side effects may include nervousness, poor concentration, nausea, and vomiting. Serious effects such as worsening of asthma may occur if one has a history of asthma. Discuss side effects with a doctor.
    • Peramivir is given as a single dose intravenously and is currently U.S. FDA approved and recommended for young adults 18 years and older.
    • Antiviral drugs are not a substitute for the flu vaccine. Getting the annual seasonal flu vaccine is still the best way to prevent the flu.

When the lungs get infected, causing pneumonia, other antiviral drugs such as ribavirin (Copegus, Rebetol) and sometimes antibiotics may be needed.

  • For nasal congestion, a doctor may suggest the use of over-the-counter decongestants. Anyone with high blood pressure, heart disease, diabetes, thyroid disease, enlarged prostate, glaucoma (high pressure inside the eye), or pregnancy should not use decongestants without a doctor's advice.
  • Phenylephrine (Neo-Synephrine) and oxymetazoline hydrochloride (Neo-Synephrine 12 Hour, Afrin) are available as nasal sprays or drops. Use two to three sprays in each nostril as indicated on the label. Only use these nasal sprays or drops for up to three days. If they are used for more than that, the medication can actually worsen the congestion. These medications are not recommended for children.
  • Pseudoephedrine (Sudafed) may also help congestion and is given by tablet. It may interact with certain foods and quite a few medications, elevate blood pressure and heart rate, and cause other serious side effects. People with chronic health conditions or on medications should consult a pharmacist or their doctor before using pseudoephedrine.

Flu in Adults Follow-up

Generally, no follow-up is needed for most flu cases unless fever or cough returns along with other new symptoms, which could signal a complication.

Is It Possible to Prevent Flu in Adults?

Personal Hygiene

  • Limit touching high-touch surfaces where flu viruses may remain alive; examples include handrails, doorknobs, faucets, keyboards, and elevator buttons.
  • Wash your hands often, especially after touching high-touch surfaces, being in public places, or at work.
  • Avoid touching your eyes, nose, or mouth before washing one's hands.
  • Avoid close contact with people who appear ill.
  • Do not share clothes or other personal items with another person during a flu outbreak.
  • Those infected with influenza should stay at home for 24 hours after fevers have resolved.

Flu Vaccination

The best means of preventing the flu is getting an influenza vaccination. The CDC recommends an annual flu vaccine for everyone 6 months of age and older. Two general types of vaccines are available. One is the injectable vaccine (known as the flu shot) made from inactivated virus. The flu shot contains only killed influenza viruses A and B.

The other is a live attenuated, or weakened, virus that is squirted into the nose. This is called intranasal vaccine or nasal spray vaccine. The intranasal form is indicated for certain people who may prefer it to a shot, and it is approved for people from 2 through 49 years of age. It is not recommended for people who are immunosuppressed or have other conditions (see below for a list). There have been concerns about poorer effectiveness than injected vaccines, however, and the Advisory Committee on Immunization Practices (ACIP) recommended against its use during flu seasons in 2016-17 and 2017-18.

There are different injected flu vaccines, such as the quadrivalent flu shot, which contains two type A viruses and two type Bs rather than the standard trivalent that has two type As and one type B. There is a high-dose shot formulation for people over 65 years of age and an intradermal (into the skin) version for people ages 18-65, and it uses a tiny needle. In August 2014, the FDA approved Afluria, which is injected into the muscle through a needle-free jet injector. A complete listing of flu vaccines that are currently available can be found at http://www.immunize.org/catg.d/p4072.pdf.

An important point is that no one vaccine is recommended over the others and one should not delay getting vaccinated in order to wait for one of the others if there is a vaccine available.

It is also important to note a widely circulated study that reported a weak, inconclusive link of flu vaccination with miscarriage; in essence, there was a slightly higher number of miscarriages in a group of women who received flu vaccine compared to usual, but there was no evidence that the vaccine caused this. Because the risk of serious flu complications and death during pregnancy is clear and far higher, the American College of Obstetricians and Gynecologists (ACOG) recommends flu vaccination as an essential part of prenatal care.

Lastly, research has shown that flu vaccination is safe in most people who have all but the most severe egg allergy. People who can eat lightly cooked eggs, for example, are not likely to be allergic to eggs. People who have only experienced hives after exposure to eggs can receive any of the licensed flu vaccines that are approved for their age and health. They may also receive the vaccine at any facility licensed to give it, such as a local pharmacy or health fair.

People who have had reactions more severe than hives after eating eggs may receive any licensed flu vaccine, but they should receive it in a facility that is staffed with health professionals and equipped to manage severe allergic reactions. This need not be a doctor's office or hospital, nor is there a prescribed 30 minute observation period after receiving the vaccine. Health professionals giving vaccines to anyone should be able to recognize severe allergic reactions. Symptoms and signs may include throat or tongue swelling, lightheadedness, repeated vomiting, or difficulty breathing, and may require the use of epinephrine or emergency medical treatment.

The influenza vaccine is given every year prior to flu season. Immunity to the flu virus develops after about two weeks. The CDC recommends that vaccine be given starting as soon as it becomes available each fall.

  • Because of substantial vaccine distribution delays during previous influenza seasons and the possibility of similar delays in the future, it is recommended that anyone at high risk for complications from the flu get a flu shot as early as September. This same group of people can still get the vaccine throughout the flu season if they were unable to be vaccinated earlier.
  • The vaccine is effective in about 70%-90% of those who get the shot, especially in older people. Not only does it decrease the risk of getting flu infection, but it can also decrease the number of visits to a doctor's office, hospitalizations, and risk of death from the flu virus. However, in some years, the vaccine is less effective because the circulating flu virus has genetically changed from the ones anticipated and included in the vaccine. The 2014-15 flu vaccine was only 23% effective due to changes in the circulating flu virus that season.

What About Side Effects From the Flu Vaccine? What if I Always Get the Flu After I Get the Flu Vaccine?

Flu vaccines cannot give you an influenza infection. The vaccines are made with flu viruses that have been inactivated and are not able to infect humans or with vaccines that only contain particles of flu virus.

As is expected, they do stimulate your immune system into thinking you have the flu, so that your body produces protective antibody within two to three weeks. Feelings of sore arm or flu-like illness within two weeks are often a sign of a good immune response; these symptoms may last one or two days.

Secondly, flu-like symptoms within two weeks of vaccine may indicate infection with influenza before antibodies have developed or infection by one of the hundreds of other viruses circulating at the same time.

No medical intervention is 100% perfect, and each strain in a vaccine may produce different levels of immunity. Therefore, it is certainly possible to get flu after antibodies have developed, usually from a different strain or a strain that has mutated from the original strain the vaccine was made for. This has happened occasionally because influenza viruses may change slightly even within the same flu season.

In either case, the influenza illness is likely to be less severe and less likely to be complicated compared to not getting the vaccine. Any protection is better than no protection, especially if you are in a high-risk group.

Who Should Get the Flu Vaccine?

Vaccination for the flu each year is recommended for all people over 6 months of age. Those at higher risk should be especially sure to get vaccinated. These include the following:
  • Anyone older than 50 years of age
  • A person of any age with chronic diseases of the heart, lungs, or kidneys
  • People with obesity or diabetes
  • Those who are HIV positive or who have AIDS
  • Women who are more than 14 weeks pregnant during the flu season (Women who are pregnant at any stage of their pregnancy and have a risk of complications from the flu should get the vaccine irrespective of how far they are into the pregnancy. Breastfeeding women can also get the flu shot without worry about harm to the baby.)
  • Residents of nursing homes and other facilities of long-term care
  • Children older than 6 months of age who have chronic heart or lung conditions, including asthma
  • Children older than 6 months of age who need regular medical care or had to be in a hospital because of metabolic diseases (such as diabetes), chronic kidney disease, or weakened immune systems (including immune system problems caused by medicine or by infection with human immunodeficiency virus [HIV/AIDS])
  • Children and teenagers (6 months to 18 years of age) who are on long-term aspirin therapy and therefore could develop Reye's syndrome after a flu illness
  • Health care professionals and volunteers who work with high-risk patients, including employees of nursing homes and chronic care facilities
  • Household members (including children) of people in high-risk groups
  • Students or others living in institutional settings (for example, those who reside in dormitories or camps where close contact is likely)
  • Anyone interested in reducing the risk of getting the flu
  • The intranasal or live vaccine (FluMist and others) is an alternative to the flu shot in people who are healthy, 2-49 years of age, and not pregnant. Exceptions are health care professionals who care for severely immunosuppressed patients or people caring for children younger than 6 months of age, children age 2 through 4 with asthma, and children age 2-17 on long-term aspirin treatment.
  • People who are allergic to eggs or who have had Guillain-Barré syndrome (paralysis) within six weeks of a prior vaccination should check with their doctor before getting an influenza vaccine.
  • People who have had severe allergic reaction to flu vaccine itself should not receive flu vaccine even if they have risk factors for severe influenza. These individuals should ask their doctor if preventive antiviral therapy may be of benefit to them.

Updates on the seasonal flu vaccine are available on the CDC web site, influenza (flu) (http://www.flu.gov).

How Effective Is the Flu Shot?

  • Vaccination remains the most effective way to prevent the flu.
  • The effectiveness varies according to the age and health of the person receiving it and the closeness that it matches the strain that is circulating in any given year.
  • Numerous studies have shown that the flu shot can reduce hospitalizations from flu from 52% to 92% in various populations, such as adults with chronic health problems like diabetes, chronic lung disease, and heart disease as well as in older adults, infants, and pregnant women.
  • People who do get the flu despite receiving the flu shot may have a milder and shorter illness.

Flu Chemoprophylaxis

Annual influenza vaccination is the best way to prevent getting the flu, but for those who are at high risk and are unvaccinated, taking oseltamivir or zanamivir after exposure can also help prevent disease. Due to concerns that the flu virus may develop resistance to these drugs, widespread use of antiviral medication to prevent the flu is not recommended. In certain instances, for example, people with severe immunodeficiency who cannot receive flu vaccine or in whom it may not work, high-risk individuals exposed to flu, or residents of a health care facility or nursing home in which there is an influenza outbreak, may take oseltamivir or zanamivir for seven days to prevent the flu.

What Is Avian Flu, and Why Is It Important?

Influenza virus is one of the few viruses that infects humans and other species like birds and pigs. Waterfowl in the wild, such as geese and gulls, are natural species for influenza A strains. Some strains are highly pathogenic (very likely to cause disease) and highly contagious in birds and produce almost 100% death rates within days; these strains cause severe epidemics on poultry farms. Not only do they cause economic losses to farming, but they pose a potential for spreading to humans if the virus changes to a variant for which human infection becomes possible. This could lead to the ability to spread from human to human and could spark a global human pandemic with a highly lethal flu, so these events are closely tracked. H5 avian flu strains have occasionally spread to humans, with 50% mortality (death rate) and severe pneumonia, but human-to-human spread has been highly limited.

What Is Swine Flu, and Why Is It Important?

Similar to avian flu viruses, there are influenza A strains that typically infect pigs. On occasion, variants of swine flu have developed the ability to infect humans, such as those who raise and work with pigs. Rarely, like avian flu, a swine flu strain has spread from pigs to humans at petting zoos or a pig farm, and some human-to-human spread has occurred. These are referred to as variant strains. An example of a swine flu variant that has spread to humans is H2N3 variant or H2N3v.

Epidemics are usually limited to a continent and occur yearly due to small changes in flu strains (antigenic drift). Pandemics spread globally and occur due to major changes in a strain (antigenic shift). Before the flu vaccine became widely used, pandemics occurred about every 20 years. This is now much less frequent but remains a risk.

Pigs may play a unique role because they can be infected with human, pig, and bird flu strains at the same time. Infection in a pig creates an opportunity for a bird strain to share genes with a flu strain that spreads easily from person to person. This can create a new human strain that sparks a global pandemic. This occurred in 2009 when an H1N1 strain caused the first pandemic since the deadly Spanish Flu pandemic of 1918. The Spanish Flu killed people within days. Between 20-40 million people died from flu worldwide, far more than those who died because of World War I during those years, and more than those who died during the Black Plague in the Middle Ages. Fortunately, the 2009 H1N1 strain was not as severe as Spanish Flu, but it did cause unexpectedly serious complications in younger individuals, obese people, and pregnant women, and it continues to circulate yearly, including during the summer.

The most important preventive tools against pandemics are vaccination against circulating strains every year and ongoing public health surveillance.

More Flu Prevention Tips

  • Travel: The risk of getting the flu during travel depends on the destination and time of the year when travel is done. In countries in the northern hemisphere, such as the United States, influenza occurs between November and March. In the southern hemisphere, most influenza occurs between April and September. In the tropical regions, such as the Caribbean, the flu occurs year-round. For people who are traveling, the recommendations are as follows:
    • Because the availability of the vaccine in North America is limited in the summer season, those needing the vaccine for travel purposes should discuss the best option for flu prevention, vaccine versus carrying of antiviral medications, with their doctor.
    • Those who are at high risk of getting complications from the flu and anyone who wants to decrease the chances of getting the flu and is visiting the tropics or the southern hemisphere from April through September should take the vaccine at least two weeks before departure if they were not vaccinated in the previous winter or fall.
    • Anyone at high risk who received the previous season's vaccine should be revaccinated before travel in the fall or winter with the current vaccine.
    • Those who have missed the flu shot can still get the vaccine during an outbreak. However, the best method of prevention is to get the shot prior to the flu season.
    • For more travel information, check the CDC National Center for Infectious Diseases Infectious Disease Information, Influenza (Flu, Influenza Virus Infection).
  • Side effects: The most frequent side effects of vaccination are soreness and redness at the vaccination site that may last for up to two days. These reactions are generally mild and rarely interfere with the ability to conduct usual daily activities. Fever, weakness, muscle aches, and other symptoms can occur, most often in children, following vaccination. These reactions begin six to 12 hours after vaccination and can last for one to two days.
    • Side effects from the intranasal vaccine are usually mild. The viruses in the nasal-spray vaccine are weakened and will not cause severe symptoms often associated with influenza illness. In children, side effects can include runny nose, headache, vomiting, muscle aches, and fever. In adults, side effects can include runny nose, headache, sore throat, and cough.
    • Most licensed flu vaccine is prepared using hens' eggs, and it is possible for them to contain very tiny amounts of egg proteins. Life-threatening allergic reactions are very rare but can be unpredictable in people who are genuinely allergic to eggs. Thus, people with egg allergy have been cautioned about flu vaccination for several years. However, there no longer significant restrictions related to egg allergy and flu vaccines.
    • People who develop more than just hives after eating eggs should receive the flu vaccine in a medical facility that is equipped to treat severe allergic reactions. Because allergic reactions may begin up to a day after an exposure, a 30-minute observation period after vaccination is no longer required.
    • Anyone who can eat soft cooked eggs without hives can get a flu vaccine.
    • Of course, those who have had a serious allergic reaction to a previous dose of flu vaccine should not receive it again.
  • Myths about the flu vaccine
    • It's not true that you can get the flu from the shot. You cannot get the flu from the shot. The shot contains only an inactivated (killed) form of the virus and therefore cannot cause influenza. The intranasal vaccine (squirted into the nose) contains live virus, but it is weakened to the point where it cannot cause disease in healthy people.
    • It is not true that you only need to have the vaccine once in your life. The flu shot must be taken every year in order to keep from getting the flu. The fact that influenza viruses continually change their structure is one of the reasons the vaccine must be taken every year. Antibodies formed by the body's immune system after the vaccination decline over time. Thus, one's own defenses may not be effective for the next flu season. Each year, the vaccine is updated to include the most current influenza virus subtype.
  • Even if you have a flu shot, you may still get the flu when the flu season arrives because the vaccine is not 100% effective in preventing the flu. The virus can be of a different subtype, so you may not be protected against it. The vaccine is made from the virus subtypes that were prevalent in the previous flu season and are predicted to be circulating in the current season. Sometimes the new vaccine may not match the all the virus types that are causing flu the next year, as was the case for the 2014-15 flu vaccine.
  • People at high risk for complications from the flu, and who have not had the shot in time to be protected, can be given one of the antiviral medications for prevention during an outbreak. Only oseltamivir and zanamivir are currently recommended for this purpose.

What Is the Prognosis of Flu in Adults?

Flu symptoms start to go away after two to five days. Fever may last for up to five days, while other symptoms, including weakness and fatigue, may persist for several weeks. The very young, the very old, and those in the high-risk groups are at risk for complications requiring hospitalization. Some people may die from the flu.

Where Can People Find More Information About the Flu?

Centers for Disease Control and Prevention, Influenza (Flu)

Flu.gov, Seasonal Influenza

National Institute of Allergy and Infectious Diseases, National Institutes of Health, Flu Fact Sheet

American Lung Association, Influenza (Flu)

Reviewed on 1/9/2018

REFERENCES:

Jefferson, T., et al. "Neuraminidase inhibitors for preventing and treating influenza in healthy adults and children." Cochrane Database Syst Rev 4 Apr. 10, 2014:CD008965. doi: 10.1002/14651858.CD008965.pub4.

Mandell, Douglas, John E. Bennett, and Raphael Dolin. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. Seventh Edition. "Influenza Viruses, Including Avian Influenza and Swine Influenza." Philadelphia: Churchill Livingstone Elsevier, 2010.

Switzerland. World Health Organization. "Influenza." <http://www.who.int/topics/influenza/en/>.

United States. Centers for Disease Control and Prevention. "Seasonal Influenza (Flu)." <http://CDC.gov/flu>.

United States. Department of Health & Human Services. "Seasonal Flu."

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