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Influenza Disease

Although many people think of influenza as the “flu” or just a common cold, it is really a specific and serious respiratory disease that can result in hospitalization and death. Hundreds of children die of influenza almost every flu season. Typical influenza disease is characterized by abrupt onset of fever, aching muscles, sore throat, and non-productive cough. Additional symptoms may include runny nose, headache, a burning sensation in the chest, eye pain and sensitivity to light. Typical influenza disease does not occur in every infected person. Someone who has been previously exposed to similar virus strains (through natural infection or vaccination) is less likely to develop serious clinical illness.

The most frequent complication of influenza is bacterial pneumonia. Viral pneumonia is a less common complication but has a high fatality rate. Other complications include inflammation of the heart and worsening of pulmonary diseases (e.g., bronchitis). Reye’s syndrome is a complication that occurs almost exclusively in children—patients suffer from severe vomiting and confusion, which may progress to coma because of swelling of the brain. To decrease the chance of developing Reye’s syndrome, infants, children, and teenagers should not be given aspirin for fever reduction or pain relief.

Viruses cause influenza. There are two basic types, A and B, which can cause clinical illness in humans. Their genetic material differentiates them. Influenza A can cause moderate to severe illness in all age groups and infects humans and other animals. Influenza B usually causes milder disease and affects only humans, primarily children.

Subtypes of the type A influenza virus are identified by two antigens on the surface of the virus. These antigens can change, or mutate, over time. When a “shift” (major change) occurs, a new influenza virus is born and an epidemic is likely among the unprotected population. This happened when the novel H1N1 influenza virus appeared in March of 2009 and led to a major pandemic, lasting until the summer of 2010.

Influenza is transmitted from person to person by airborne droplets formed during coughing and sneezing. The droplets are then inhaled or land on mucus membranes (lining of the nose or inside of the mouth or the conjunctiva of the eye). Influenza virus also can be transmitted orally. A person is most likely to pass on the virus during the period beginning one to two days before the onset of symptoms and ending four to five days after the onset. The incubation period of influenza is usually two days but can range from one to four days. For most people, the flu lasts only a few days, but some people get much, much sicker. Influenza is of particular concern in people with pre-existing heart and/or lung conditions, the elderly, children under 2 years of age and pregnant women.


Vaccination is the principal means of preventing influenza and its complications. Here are some additional steps that may help prevent the spread of respiratory illnesses like influenza:

  • Cover your nose and mouth with your sleeve or a tissue when you cough or sneeze—throw the tissue away after you use it.
  • Wash your hands often with soap and water, especially after you cough or sneeze. If you are not near water, use an alcohol-based hand cleaner.
  • Stay away as much as you can from people who are sick.
  • If you get influenza, stay home from work or school for at least 24 hours after the fever has ended. If you are sick, don’t go near other people to avoid infecting them.
  • Try not to touch your eyes, nose, or mouth. Germs often spread this way.


The most effective way to avoid an infection with influenza is to receive the influenza vaccine every year. Influenza vaccines are safe and effective, and they do not cause the flu. Because the influenza virus characteristically changes or mutates from year to year, it is necessary to prepare a new vaccine each year for protection from the new flu strains that are present that year. For this reason it is essential that everyone get immunized against the seasonal flu every year because last year’s vaccine may not be protective against this year’s virus strains. Also, the protection given by the vaccine can wane over time so that last year’s vaccination may not continue to be protective, particularly for individuals age 65 and older.

Flu vaccine protection 2017—What Is Best for You?

The latest update from the Advisory Committee on Immunization Practices (ACIP) of the CDC is now published. Here is why it matters. No flu season is the same. It is impossible to predict when the flu season will peak. We have lots of people to vaccinate—everyone 6 months and older—and there is a plethora of flu vaccine choices

CDC recommends that everyone aged 6 months or older receive an influenza vaccine every year, by the end of October if possible. However, significant seasonal influenza virus activity can continue into May, so vaccination later in the season can still be beneficial.

Only injectable influenza vaccines are recommended for use during the 2017-2018 season. Live attenuated influenza vaccine (LAIV; also known as the nasal spray vaccine) is not recommended again this season because of concerns about lack of effectiveness against (H1N1) viruses.

Recommended 2017-2018 influenza vaccines include a number of inactivated injectable vaccines as well as recombinant influenza vaccines. Both trivalent and quadrivalent injectable vaccines will be available this season. CDC and the Advisory Committee on Immunization Practices (ACIP) do not have a preferential recommendation for one influenza vaccine product over another. Don't delay vaccination if quadrivalent vaccine is not available. Both types of vaccine offer important protection from influenza.

Trivalent vaccines are designed to protect against three different influenza viruses. Quadrivalent influenza vaccines protect against the same three viruses plus an additional B virus from a different lineage of influenza B viruses. The composition of this season's vaccines has been updated to better match recently circulating influenza viruses.

For the 2017-2018 season, US trivalent influenza vaccines will contain: An A/Michigan/45/2015 (H1N1)pdm09–like virus;
An A/Hong Kong/4801/2014 (H3N2)–like virus; and
a B/Brisbane/60/2008–like virus, which is from the Victoria lineage of B viruses.

Quadrivalent vaccines will include an additional vaccine virus strain, a B/Phuket/3073/2013–like virus from the Yamagata lineage. This composition reflects a change in the H1N1 component from the previous season.

Special Populations

As of June 2017, pregnant women can receive any licensed, recommended, and age-appropriate influenza vaccine. This now includes quadrivalent and trivalent recombinant vaccines as options for pregnant women aged 18 years and older, in addition to age-appropriate inactivated influenza vaccines.

As in previous seasons, children aged 6 months through 8 years who have never been vaccinated against influenza, or for whom vaccination history is unknown, will require two doses of influenza vaccine, administered at least 4 weeks apart, for full protection. Similar to last year, if a child has received two or more doses of trivalent or quadrivalent influenza vaccine in the years before July 1, 2017, only one dose of 2017- 2018 flu vaccine is recommended.

Lastly, a word about recommendations for influenza vaccination of persons with egg allergy, which have not changed since last season. As a reminder, ACIP removed the recommendation that egg-allergic recipients should be observed for 30 minutes following vaccination for signs and symptoms of an allergic reaction. As a reminder, providers should consider observing all patients for 15 minutes after administration of any vaccine to decrease the risk for injury should the recipient experience syncope, per the General Best Practices Guidelines on Immunization. Also, persons with a history of severe allergic reaction to egg (i.e., any symptom other than hives) should be vaccinated in an inpatient or outpatient medical setting under the supervision of a healthcare provider who is able to recognize and manage severe allergic conditions.

Primary Immunodeficiency Family Plan

For families with a member who has a primary immunodeficiency disease (PI), we recommend that all members of the family should be given the inactivated (killed) vaccine. The vaccines usually become available in August or September. Studies have shown that immunization can still be effective when given well into February or March in some years, so it is important to ask for the vaccine even if the New Year has passed.

Why do we recommend that everyone be immunized? First, some patients with a PI may benefit from the vaccine. Even if they do not, there is little down side to receiving the inactivated vaccine. Family members who are able to respond to the vaccine will be protected. Even if the patient with PI does not respond to the immunization, he or she will benefit from having everyone else in the family protected from infection and not susceptible to bringing the virus home with them. We want to create a “protective cocoon” of immunized persons surrounding our patients so that they have less chance of being exposed. It would be a good strategy to encourage employers to provide influenza immunization programs at the place of work and schools to similarly encourage immunization of the student body to further extend this “cocoon.”

Individuals with PI have the same risk of contracting flu as does the rest of the population. The same type of anti-viral medicine, i.e., Tamiflu or Relenza, which is effective for people with normal immune systems, would be effective for patients with PI who get influenza. Note that immunoglobulin (Ig) replacement therapy may not protect against newly emerged strains of the influenza virus since the Ig contained in the currently available lots of IVIG or SCIG was obtained from donors several months ago, probably before the newer strains of influenza had circulated through the donor population to result in specific antibody formation.

Influenza can be diagnosed rapidly by a test done in physician offices. If the test is positive, it is recommended that persons immediately begin anti-virus treatment. Speed is important in this situation since the antiviral medications are most effective if begun within 48 hours of the onset of the illness. It would be a good idea to discuss with your physician plans for dealing with influenza before you get sick so that you are prepared. If you do become ill, you should contact your doctor immediately about initiating treatment. However, it would be wise to contact your physician first, before going to their office, an urgent care facility or emergency room.

During the flu season, you may want to stay away from crowded public places, such as shopping malls, if you are concerned about exposure. Most people can get information from the national media and from their physicians on other ways to prevent exposure, as well as when to use additional precautionary measures.

What do I do if there is influenza in the schools or at my workplace?

There is no single recommendation that is applicable to every situation. Some medical advisors recommend that unless influenza is in their classroom children with PI should go to school. If there is a known direct contact with secretions from a flu-affected child or adult by the individual with PI, some medical advisors suggest that the patient should go on Tamiflu once a day for 10 days. If the individual with PI develops symptoms of influenza, that person should be treated with Tamiflu twice a day for 5 days. Relenza could also be used as the anti-viral treatment. The same treatment recommendations should apply to adults with Common Variable Immune Deficiency (CVID) or other types of PI. If you have any questions, please contact your specialist.

For more, updated information on the flu, visit the CDC website: or

Revised: September 2017