CDC - Seasonal Influenza (Flu) - Key Facts About Seasonal Flu Vaccine

October 25, 2013

The flu vaccine cannot cause the flu. The viruses in the vaccine are either killed or weakened, which means they cannot cause infection.
If given during pregnancy, the flu shot has been shown to protect both the mother and her baby (up to age 6 months) from flu.
You can take 3 steps to fight flu: get vaccinated, practice healthy habits, and take antiviral medications if prescribed.

Please share this email with others interested in improving public health practice through evidence-based strategies. A library of "Did You Know?" information is available online.

Key Facts About Seasonal Flu Vaccine

Flu Vaccination

Why should people get vaccinated against the flu?

Influenza is a serious disease that can lead to hospitalization and sometimes even death. Every flu season is different, and influenza infection can affect people differently. Even healthy people can get very sick from the flu and spread it to others. Over a period of 31 seasons between 1976 and 2007, estimates of flu-associated deaths in the United States range from a low of about 3,000 to a high of about 49,000 people. During a regular flu season, about 90 percent of deaths occur in people 65 years and older. The “seasonal flu season” in the United States can begin as early as October and last as late as May.
During this time, flu viruses are circulating in the population. An annual seasonal flu vaccine (either the flu shot or the nasal-spray flu vaccine) is the best way to reduce the chances that you will get seasonal flu and spread it to others. When more people get vaccinated against the flu, less flu can spread through that community.

How do flu vaccines work?

Flu vaccines cause antibodies to develop in the body about two weeks after vaccination. These antibodies provide protection against infection with the viruses that are in the vaccine.
The seasonal flu vaccine protects against the influenza viruses that research indicates will be most common during the upcoming season. Traditional flu vaccines (called trivalent vaccines) are made to protect against three flu viruses; an influenza A (H1N1) virus, an influenza A (H3N2) virus, and an influenza B virus. In addition, this season, there are flu vaccines made to protect against four flu viruses (called “quadrivalent” vaccines). These vaccines protect against the same viruses as the trivalent vaccine as well as an additional B virus.

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What kinds of flu vaccines are available?

There are several flu vaccine options for the 2013-2014 flu season.
Traditional flu vaccines made to protect against three different flu viruses (called “trivalent” vaccines) are available. In addition, this season flu vaccines made to protect against four different flu viruses (called “quadrivalent” vaccines) also are available.
The trivalent flu vaccine protects against two influenza A viruses and an influenza B virus. The following trivalent flu vaccines are available:

Standard dose trivalent shots that are manufactured using virus grown in eggs. These are approved for people ages 6 months and older. There are different brands of this type of vaccine, and each is approved for different ages. However, there is a brand that is approved for children as young as 6 months old and up.
A standard dose trivalent shot containing virus grown in cell culture, which is approved for people 18 and older.
A standard dose trivalent shot that is egg-free, approved for people 18 through 49 years of age.
A high-dose trivalent shot, approved for people 65 and older.
A standard dose intradermal trivalent shot, which is injected into the skin instead of the muscle and uses a much smaller needle than the regular flu shot, approved for people 18 through 64 years of age.

The quadrivalent flu vaccine protects against two influenza A viruses and two influenza B viruses. The following quadrivalent flu vaccines are available:

A standard dose quadrivalent shot
A standard dose quadrivalent flu vaccine, given as a nasal spray, approved for healthy* people 2 through 49 years of age

(*”Healthy” indicates persons who do not have an underlying medical condition that predisposes them to influenza complications.)

CDC does not recommend one flu vaccine over the other. The important thing is to get a flu vaccine every year.

Are any of the available flu vaccines recommended over others?

No. CDC does not recommend one flu vaccine over another. This includes deciding between trivalent or quadrivalent vaccine or between injection (the flu shot) or nasal spray vaccine. The important thing is to get a flu vaccine every year. Talk to your doctor or nurse about the best options for you and your loved ones.

Who should get vaccinated this season?

Everyone who is at least 6 months of age should get a flu vaccine this season. This recommendation has been in place since February 24, 2010 when CDC’s Advisory Committee on Immunization Practices (ACIP) voted for “universal” flu vaccination in the United States to expand protection against the flu to more people.
While everyone should get a flu vaccine this season, it’s especially important for some people to get vaccinated.
Those people include the following:

People who are at high risk of developing serious complications (like pneumonia) if they get sick with the flu.
- People who have certain medical conditions including asthma, diabetes, and chronic lung disease.
- Pregnant women.
- People younger than 5 years (and especially those younger than 2), and people 65 years and older.
- A complete list is available at People Who Are at High Risk of Developing Flu-Related Complications.
People who live with or care for others who are at high risk of developing serious complications (see list above).
- Household contacts and caregivers of people with certain medical conditions including asthma, diabetes, and chronic lung disease.
- Household contacts and caregivers of infants less than 6 months old.
- Health care personnel.

More information is available at Who Should Get Vaccinated Against Influenza.

Special Consideration Regarding Egg Allergy:

People who have ever had a severe allergic reaction to eggs may be advised not to get vaccinated. People who have had a mild reaction to egg—that is, one which only involved hives—may receive a flu shot with additional precautions. Make sure your health care provider knows about any allergic reactions. Most, but not all, types of flu vaccine contain small amount of egg.

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Who Should Not Be Vaccinated?

Influenza vaccine is not approved for children younger than 6 months of age.
People who have had a severe allergic reaction to influenza vaccine should generally not be vaccinated.
There are some people who should not get a flu vaccine without first consulting a physician.
These include:

People who have a moderate-to-severe illness with or without a fever (they should wait until they recover to get vaccinated), and
People with a history of Guillain–Barré Syndrome (a severe paralytic illness, also called GBS) that occurred after receiving influenza vaccine and who are not at risk for severe illness from influenza should generally not receive vaccine. Tell your doctor if you ever had Guillain-Barré Syndrome. Your doctor will help you decide whether the vaccine is recommended for you.

When should I get vaccinated?

Flu vaccination should begin soon after vaccine becomes available, ideally by October. However, as long as flu viruses are circulating, vaccination should continue to be offered throughout the flu season, even in January or later. While seasonal influenza outbreaks can happen as early as October, most of the time influenza activity peaks in January or later. Since it takes about two weeks after vaccination for antibodies to develop in the body that protect against influenza virus infection, it is best that people get vaccinated so they are protected before influenza begins spreading in their community.
Flu vaccine is produced by private manufacturers, so availability depends on when production is completed. Shipments began in late July and August and will continue throughout September and October until all vaccine is distributed.

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http://www.flu.gov/stay-connected/vaccinelocator_2011.html

Where can I get a flu vaccine?

Flu vaccines are offered in many locations, including doctor’s offices, clinics, health departments, pharmacies and college health centers, as well as by many employers, and even in some schools.
Even if you don’t have a regular doctor or nurse, you can get a flu vaccine somewhere else, like a health department, pharmacy, urgent care clinic, and often your school, college health center, or work.
The following Vaccine Locator

is a useful tool for finding vaccine in your area.

Why do I need a flu vaccine every year?

A flu vaccine is needed every year because flu viruses are constantly changing. It’s not unusual for new flu viruses to appear each year. The flu vaccine is updated annually to keep up with the flu viruses as they change.
Also, multiple studies conducted over different seasons and across vaccine types and influenza virus subtypes have shown that the body’s immunity to influenza viruses (acquired either through natural infection or vaccination) declines over time.

Does flu vaccine work right away?

No. It takes about two weeks after vaccination for antibodies to develop in the body and provide protection against influenza virus infection. That’s why it’s better to get vaccinated early in the fall, before the flu season really gets under way.

Can I get seasonal flu even though I got a flu vaccine this year?

Yes. There is still a possibility you could get the flu even if you got vaccinated. The ability of flu vaccine to protect a person depends on various factors, including the age and health status of the person being vaccinated, and also the similarity or “match” between the viruses used to make the vaccine and those circulating in the community. If the viruses in the vaccine and the influenza viruses circulating in the community are closely matched, vaccine effectiveness is higher. If they are not closely matched, vaccine effectiveness can be reduced. However, it’s important to remember that even when the viruses are not closely matched, the vaccine can still protect many people and prevent flu-related complications. Such protection is possible because antibodies made in response to the vaccine can provide some protection (called cross-protection) against different but related influenza viruses. For more information about vaccine effectiveness, visit How Well Does the Seasonal Flu Vaccine Work?

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Vaccine Effectiveness

Influenza vaccine effectiveness (VE) can vary from year to year and among different age and risk groups. For more information about vaccine effectiveness, visit How Well Does the Seasonal Flu Vaccine Work? For information specific to this season, visit About the Current Flu Season.

Will this season's vaccine be a good match for circulating viruses?

It's not possible to predict with certainty which flu viruses will predominate during a given season. Over the course of a flu season, CDC studies samples of flu viruses circulating during that season to evaluate how close a match there is between viruses used to make the vaccine and circulating viruses. Data are published in the weekly FluView. In addition, CDC conducts studies each year to determine how well the vaccine protects against illness during that season. The results of these studies are typically published following the conclusion of the flu season and take into consideration all of the data collected during the season. Interim studies also may be conducted that provide preliminary estimates of the vaccine’s benefits that season using data available at that time. For more information, see Vaccine Effectiveness – How Well Does the Flu Vaccine Work?
Flu viruses are constantly changing (called “antigenic drift”) – they can change from one season to the next or they can even change within the course of one flu season. Experts must pick which viruses to include in the vaccine many months in advance in order for vaccine to be produced and delivered on time. (For more information about the vaccine virus selection process visit Selecting the Viruses in the Influenza (Flu) Vaccine.) Because of these factors, there is always the possibility of a less than optimal match between circulating viruses and the viruses in the vaccine.

Can the vaccine provide protection even if the vaccine is not a "good" match?

Yes, antibodies made in response to vaccination with one flu virus can sometimes provide protection against different but related viruses. A less than ideal match may result in reduced vaccine effectiveness against the virus that is different from what is in the vaccine, but it can still provide some protection against influenza illness.
In addition, even when there is a less than ideal match or lower effectiveness against one virus, it's important to remember that the flu vaccine may protect against the other flu viruses included in the vaccine.
For these reasons, even during seasons when there is a less than ideal match, CDC continues to recommend flu vaccination. This is particularly important for people at high risk for serious flu complications, and their close contacts.

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Vaccine Side Effects (What to Expect)

Can the flu vaccine give me the flu?

No, a flu vaccine cannot cause flu illness. Flu vaccines that are administered with a needle are currently made in two ways: the vaccine is made either with a) flu vaccine viruses that have been ‘inactivated’ and are therefore not infectious, or b) with no flu vaccine viruses at all (which is the case for recombinant influenza vaccine). The nasal spray flu vaccine does contain live viruses. However, the viruses are attenuated (weakened), and therefore cannot cause flu illness. The weakened viruses are cold-adapted, which means they are designed to only cause infection at the cooler temperatures found within the nose. The viruses cannot infect the lungs or other areas where warmer temperatures exist.
Different side effects can be associated with the flu shot and nasal spray flu vaccines. These side effects are mild and short-lasting, especially when compared to symptoms of influenza infection.
The flu shot: The viruses in the flu shot are killed (inactivated), so you cannot get the flu from a flu shot. Some minor side effects that could occur are:

Soreness, redness, or swelling where the shot was given
Fever (low grade)
Aches

The nasal spray: The viruses in the nasal spray vaccine are weakened and do not cause severe symptoms often associated with influenza illness. In children, side effects from the nasal spray can include:

Runny nose
Wheezing
Headache
Vomiting
Muscle aches
Fever

In adults, side effects from the nasal spray vaccine can include

Runny nose
Headache
Sore throat
Cough

If these problems occur, they begin soon after vaccination and are mild and short-lived. Almost all people who receive influenza vaccine have no serious problems from it. However, on rare occasions, flu vaccination can cause serious problems, such as severe allergic reactions. People who think that they have been injured by the flu shot can file a claim for compensation from the National Vaccine Injury Compensation Program (VICP)

.
More information about the safety of flu vaccines is available at Influenza Vaccine Safety.

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Vaccine Supply and Distribution

How much vaccine will be available during 2013-2014?

Manufacturers have projected that they will produce between 135 million and 139 million doses of influenza vaccine for use in the United States during the 2013-2014 influenza season. An estimated 30 million to 32 million of these doses will be quadrivalent flu vaccine. The rest will be trivalent flu vaccine.

Where can I find information about vaccine supply?

Information about vaccine supply is available on the CDC influenza web site.

Why do manufacturers and distributors take a phased approach to vaccine distribution?

Influenza vaccine production begins as early as 6-9 months before the beginning of vaccine distribution. Even with this early start, it isn’t possible to complete the entire production and distribution process prior to flu season, particularly given the limited number of influenza vaccine manufacturing plants in the United States and the large number of doses that are produced each year. Instead, influenza vaccine distribution takes place in a phased fashion over a number of months. It begins in late summer for some manufacturers and vaccine products and usually completes near the end of November or early in December. This system can leave doctors and other vaccine providers with uncertainty about when they can expect to receive their full order of vaccine and can make it difficult for them to plan their vaccination activities. Manufacturers and distributors try to get some vaccine to as many providers as possible as early as possible so that they can begin vaccinating their patients.

What role does the Department of Health and Human Services play in the supply and distribution of the seasonal influenza vaccine?

Influenza vaccine production and distribution are primarily private sector endeavors. The Department of Health and Human Services and CDC do not have the authority to control influenza vaccine distribution nor the resources to manage such an effort. However, the Department has made significant efforts to enhance production capacity of seasonal influenza vaccines, including supporting manufacturers as they invest in processes to stabilize and increase their production capacity.