Influenza Vaccine | The Children's Hospital of Philadelphia

Parents PACK

Influenza Vaccine

General information

Please visit the Vaccine Education Center for general information about influenza and the vaccine.

Additional information from past issues of the Parents PACK newsletter

Influenza: Virus, Disease and Vaccine

Influenza virus

Influenza is a highly contagious virus that infects the nose, throat, windpipe and lungs. The virus spreads through coughing, sneezing and talking.

Influenza viruses are highly susceptible to genetic changes when they reproduce in a host. Because of these changes, which most often are minor, the disease causes epidemics each year and, most years, a new vaccine is necessary to prevent infections. Periodically, one of these new influenza viruses is different enough that few or no people throughout the world are immune to it. When this happens, a pandemic occurs.

Influenza disease

People with influenza typically have:

The onset of symptoms can be sudden and severe, causing victims to remember the exact hour when they got sick.

Influenza can be particularly devastating for people with chronic conditions of the lungs, heart or kidneys; children younger than 2; adults older than 65; people living in long-term care facilities and pregnant women.

Complications caused by infection with influenza can include pneumonia, heart disease, or swelling of the brain, known as encephalitis.

Influenza vaccine

Influenza vaccines typically contain the three influenza viruses expected to cause disease that season. The vaccine is available as a shot and a nasal spray.

Both versions of the influenza vaccine are grown in eggs, so in the past, people who are allergic to eggs were not recommended to get the vaccine; however, recent studies have shown that the quantities of egg proteins in the vaccine are not sufficient to cause an allergic reaction. Nevertheless, people with egg allergies are recommended to remain at the doctor’s office for about 15 minutes after getting the vaccine just to be safe.

It takes about two weeks after getting the vaccine for immunity to develop.

Resources for additional information

Vaccine Education Center

Centers for Disease Control and Prevention (CDC)

Other helpful websites

Prevent Influenza, sponsored by the National Influenza Vaccine Summit

Families Fighting Flu (FFF)

Faces of Influenza, a campaign of the American Lung Association

Parents of Kids with Infectious Diseases (PKIDS) 
Influenza information includes a video from NPR showing how influenza spreads from one person to another and causes infection.


Winter viruses, colds and "the flu"

With winter and the holidays comes cold and flu season. We see different people, more people, and tend to stay in warm, confined places. All of these things can lead to more sicknesses. Often when people become ill during the winter, they assume they have "the flu." While symptoms for some of these illnesses are "flu-like," the cause may not be influenza. Here is a list of common winter symptoms and the viruses that can cause them:

Respiratory symptoms (congestion, runny nose, sneezing, coughing, sore throat) can be caused by:

Gastrointestinal symptoms (vomiting, nausea, diarrhea) can be caused by:

Only two of the viruses mentioned above (influenza and rotavirus) are currently preventable by immunization. Washing your hands frequently and thoroughly, getting enough rest, staying home when ill, coughing into your elbow, and eating a well-balanced diet may decrease your chances of getting sick or passing an illness to others.

And remember, if you think you have "the flu," you may not actually have influenza!


Deaths from influenza

Q. My wife and I have never had the flu shot, and some of our friends seem to get the shot and get sick. So when they say thousands of people die every year from flu, is it the people who got the flu shot or people who did not?

A. Many people who die from influenza actually die from complications related to the illness, such as pneumonia or a secondary bacterial infection. Most of these people did not have the vaccine. In some cases, people had the vaccine but it did not work well enough or at all for them. We know that for every 10 people who get the vaccine, about 6 or 8 of them will be protected from influenza. The others may still get influenza, but in most cases — not all — their disease is mild.

Finally, it is worth mentioning that some people will think they have “the flu,” but it is not actually an influenza infection; rather it’s caused by another virus that infects the respiratory tract producing similar symptoms.


Pandemic flu

Flu pandemics occur about three times every century. The most recent pandemics have occurred in 1889, 1900, 1918, 1957, 1968, and 2009. The pandemics in 1957 and 1968 each claimed four to six million lives, but the pandemic in 1918 was the most devastating. Between 50 and 100 million people died from the strain of influenza known as "Spanish flu" during that pandemic.

Nasal influenza vaccine and pregnant women

Q. Can someone who got the nasal influenza vaccine be near pregnant women?

A. Yes. Although the influenza shot and not the nasal spray is recommended for pregnant women, there is no danger associated with being around others who have received the nasal vaccine.

The theoretical concern is that the nasal version contains live, weakened influenza virus which could be transmitted to a pregnant woman and her developing baby. However, because the virus is weakened, it is not likely to cause illness in the vaccine recipients or others who may come into contact with them. Also, the nasal spray vaccine virus doesn’t reproduce itself at core body temperatures, so it can’t infect the baby.

The only people a nasal-influenza-vaccine recipient should not be around are people who are severely immune compromised, such as bone marrow transplant patients.


Preventing influenza

Washing your hands, covering your coughs and sneezes, and staying home when you are sick can help decrease the spread of influenza; however, not everyone follows these recommendations and people often spread the virus in the day or two before they feel sick. So the best chance of preventing influenza is to get immunized.


Data regarding pregnancy and the influenza vaccine

For several years, women who are pregnant during the influenza season have been recommended to receive an influenza vaccine. This recommendation was made to protect moms-to-be who are more likely to be hospitalized with an influenza infection compared with otherwise healthy women who are not pregnant.

A study published in the New England Journal of Medicine in September 2008 suggests that this recommendation may provide additional benefits. Study authors compared pregnant women who received an influenza vaccine with pregnant women who received a vaccine against pneumococcus, a bacteria that causes pneumonia, and found that not only were the women who had the influenza vaccine less likely to have respiratory illness with fever, so were their babies. 

In addition to being better protected against general respiratory illnesses, the babies whose mothers had received an influenza vaccine were also better protected against influenza. So, moms-to-be who get their influenza vaccine are not only protecting themselves, they are also protecting their unborn babies.

Subsequent studies have reproduced these findings.


Breastfeeding and the influenza vaccine

Q. If I am breastfeeding my new baby and I get the influenza vaccine, will my baby also be protected from the flu?

A. Infants who are breastfed will receive antibodies to influenza through breast milk if the mother has been vaccinated. However, an infant older than 6 months should receive an influenza vaccine, even if the baby is still breastfeeding. This will provide the baby with additional protection against influenza.

Animals that can be infected with influenza

Some diseases are only found in humans; however, influenza can infect many types of animals, such as: 


Updated: January 2013

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