Influenza:
Questions and Answers
information about the disease and vaccines
What causes influenza? cially older adults. Some people may also have nausea,
Influenza is caused by influenza viruses. Two types of vomiting, or diarrhea; these symptoms are more often
influenza, A and B, cause outbreaks in people. Both seen in children.
types can cause mild to severe illness in all age groups.
While influenza A viruses infect humans and other ani- How serious is influenza?
mals, influenza B viruses affects only humans. Although many people think of influenza as just a com-
Subtypes of type A influenza virus are identified by two mon cold, it is really a specific and serious respiratory
antigenic proteins called hemagglutinin [H] and neur- infection that can result in hospitalization and death.
aminidase [N] on the surface of the virus. These proteins Rates of infection from seasonal influenza are highest
can change, or mutate, over time. Because these pro- among children. The risks for influenza-related compli-
teins can change, people can get influenza infections cations, hospitalizations, and deaths are highest
multiple times over their lifetime. An antigen “shift” among adults ages 65 years and older, children
(major change) creates a new influenza A virus with a younger than 5 years, pregnant women, and people of
new H, or H and N, that can cause a global epidemic if any age who have medical conditions that place them
the virus can spread easily among people and if most at increased risk for complications from influenza.
people do not have immunity against it. This happened From the 2010–11 through 2019–20 seasons, the
most recently in 2009 when the novel H1N1 influenza annual influenza-related disease burden varied from
virus appeared and led to a major pandemic. 9–49 million illnesses, 4–23 million medical visits,
140,000–960,000 hospitalizations, and 12,000–61,000
How does influenza spread? deaths per year. The number of influenza laboratory-
Influenza is transmitted through the air from the respi- confirmed deaths in children reported to CDC aver-
ratory tract of an infected person when they talk, aged 132 (range 37–189) per year. This is considered
cough, or sneeze. It can also be transmitted by touch- an underestimate of actual pediatric deaths as some
ing a surface that has respiratory droplets with influ- influenza-related deaths are likely not reported or rec-
enza viruses and then touching the nose, mouth, or ognized. For more information on the health burden of
possibly eyes. influenza, see
www.cdc.gov/flu/about/burden/index.html.
How long does it take to develop symptoms of
influenza after being exposed? What are possible complications from influenza?
The most frequent complication from influenza are viral
The incubation period of influenza is usually two days
and bacterial pneumonia. Other complications include
but can range from one to four days.
inflammation of the heart (myocarditis), brain (enceph-
alitis) or muscle (myositis). Influenza also can worsen
What are the symptoms of influenza?
chronic medical conditions like cardiovascular disease,
Typical influenza disease is characterized by sudden leading to heart attacks or worsening congestive heart
onset of fever, aching muscles, sore throat, and non- failure, and worsening asthma and diabetes.
productive cough. Additional symptoms may include
Reye syndrome is a complication that occurs almost
runny nose, headache, a burning sensation in the
exclusively in children – patients suffer from severe
chest, and eye pain and sensitivity to light. Typical
vomiting and confusion, which may progress to coma
influenza disease does not occur in every infected per-
because of swelling of the brain. To decrease the chance
son. Someone who has been previously exposed to
of developing Reye syndrome, infants, children, and
similar virus strains (through natural infection or vacci-
teenagers should not be given aspirin for fever reduction
nation) is less likely to develop serious clinical illness.
or pain relief.
Not everyone with influenza illness has a fever, espe-
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, Influenza: Questions and Answers (continued) page 2 of 7
What is the best way to prevent influenza? used for both treatment and prevention (also called
The best way to prevent influenza is with annual prophylaxis). It is important to remember that antiviral
influenza vaccination. drugs are not a substitute for vaccination. CDC has
more information on the use of influenza antiviral
medications at
Is there an alternative to vaccination in preventing
www.cdc.gov/flu/professionals/antivirals/index.htm.
influenza?
No. Vaccination is the single best way to prevent influ-
If I contract influenza, what should I do?
enza and its complications. Some steps that may help Call your healthcare provider to discuss your particular
prevent the spread of respiratory illnesses, like influ- situation. If you are at high risk of developing complica-
enza, include: tions from influenza, you should consult your health-
care provider immediately if you develop influenza-like
1. Cover your nose and mouth with your sleeve or a
symptoms; you may benefit from influenza antiviral
tissue when you cough or sneeze – throw the tissue
medicine. You will need to get plenty of rest and drink
away after you use it and then wash your hands.
a lot of liquids. You can also take medications to
2. Wash your hands often with soap and water, especially relieve the symptoms of influenza (but never give aspi-
after you cough or sneeze. If you are not near water, rin to children or teenagers who have influenza-like
use an alcohol-based hand cleaner. symptoms, particularly fever). Antiviral medicines are
3. Stay away as much as you can from people who are most beneficial when started within the first 1–2 days
sick. of influenza illness. For purposes of treatment and pre-
4. If you get influenza, stay home from work or school vention, antiviral medicines are prioritized for people
for at least 24 hours after the fever has ended. If you at high risk for influenza-related complications, such as
are sick, don’t go near other people to avoid infect- people 65 years or older, people with chronic medical
ing them. conditions, pregnant women, and young children.
5. Try not to touch your eyes, nose, or mouth. Viruses When is a person with influenza contagious?
often spread this way.
A person may pass virus from 1 day before symptoms
Are any drugs available to prevent or treat influenza? start through 5–7 days after illness onset.
There are four influenza antiviral drugs recommended Can you get influenza more than once?
for use in selected patients. Oseltamivir (Tamiflu) and
inhaled zanamivir (Relenza) can be used for treatment Yes. Influenza viruses change frequently and infection
or prevention. Oral baloxavir (Xofluza) and intravenous with one strain does not provide protection against
peramivir (Rapivab) are recommended only for treat- all strains.
ment. All four provide protection against both A and B
viruses. Two other antiviral medications, amantadine When did influenza vaccine first become available?
and rimantadine which have activity only against influ- The first influenza vaccine in the United States became
enza A viruses, are not recommended for use because available in 1945.
of high levels of resistance among circulating influenza
A viruses. What kind of vaccine is it?
Use of antiviral medications can reduce the severity The most common influenza vaccine is made from
and length of influenza illness. People with severe ill- inactivated (killed) viruses that are given as an intra-
ness and people at increased risk of severe illness muscular injection. Two different influenza vaccines
(e.g., people at high risk of influenza complications, (cell-culture based inactivated vaccine and recombi-
such as young children, people with chronic medical nant influenza vaccine or RIV) are made without the
conditions, and older adults) should be treated with use of eggs. A nasal spray influenza vaccine containing
influenza antiviral medications when influenza is live viruses that have been weakened (attenuated) is
suspected. also available. Influenza vaccine in the United States
Antiviral medicine is also recommended for use in cer- contains either 3 or 4 strains of influenza virus. There
tain outbreak situations (e.g., nursing home out- is no preference for one type of vaccine over another
breaks); in such cases, antiviral medication can be for people for whom more than one recommended and
age-appropriate vaccine is available.
continued on the next page �
Immunization Action Coalition • Saint Paul, Minnesota • 651- 647- 9009 • www.immunize.org • www.vaccineinformation.org
www.immunize.org/catg.d/p4208.pdf • Item #P4208 (10/20)
