General Information
Updated: Dec 10, 2003
What kind of flu vaccines are there?
There are two types of vaccines that protect against the flu. The "flu shot" is
an inactivated vaccine (containing killed virus) that is given with a needle,
usually in the arm. A different kind of vaccine, called the nasal-spray flu
vaccine (sometimes referred to as LAIV for Live Attenuated Influenza Vaccine),
was approved in 2003. The nasal-spray flu vaccine contains attenuated (weakened)
live viruses, and is administered by nasal sprayer. It is approved for use
only among healthy people between the ages of 5 and 49 years. The flu shot
is approved for use among people over 6 months of age, including healthy
people and those with chronic medical conditions.
Each of the two vaccines contains three influenza viruses, representing one
of the three groups of viruses circulating among people in a given year. Each
of the three vaccine strains in both vaccines – one A (H3N2) virus, one A
(H1N1) virus, and one B virus – are representative of the influenza vaccine
strains recommended for that year. Viruses for both vaccines are grown in eggs.
Updated Dec 10, 2003
How do flu vaccines work?
Both flu vaccines (the flu shot and the nasal-spray flu vaccine (LAIV)) work
in the same way; they cause antibodies to develop in the body, and these antibodies
provide protection against influenza virus infection.
Updated Dec 10, 2003
Why should people get vaccinated against the flu?
Influenza is a serious disease, and people of any age can get it. In an average
year, the flu causes 36,000 deaths (mostly among those aged 65 years or older)
and more than 200,000 hospitalizations in the United States. The "flu season" in
the United States is usually from November through April each year. During
this time, flu viruses are circulating in the population. An annual flu vaccine
(either the flu shot or the nasal-spray flu vaccine) is the best way to reduce
the chances that you will get the flu.
Updated Dec 10, 2003
When should I get a flu vaccination?
Beginning each September, the flu shot should be offered to people at high
risk when they are seen by health-care providers for routine care or as a result
of hospitalization. See the ACIP
Recommendations for Using Inactivated Influenza Vaccine.
The best time to get vaccinated is from October through
November. Flu activity in the United States generally peaks
between late December and early March.
You can still benefit from getting vaccinated after November,
even if flu is present in your community. Vaccine should
continue to be offered to unvaccinated people throughout
the flu season as long as vaccine is still available. Once
you get vaccinated, your body makes protective antibodies
in about two weeks.
Updated Dec 10, 2003
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. In the meantime,
you are still at risk for getting the flu. That's why it's better to get vaccinated
early in the fall, before the flu season really gets under way.
Updated Dec 10, 2003
Can I get the flu even though I got a flu vaccine
this year?
Yes. The ability of flu vaccine to protect a person depends on two things:
1) the age and health status of the person getting the vaccine, and 2) the
similarity or "match" between the virus strains in the vaccine and those in
circulation.
Updated Dec 10, 2003
How effective is the flu vaccine?
The flu vaccine is the most effective way to prevent the flu. However, in limited
studies, the flu shot and the nasal-spray
flu vaccine (LAIV) have different rates of effectiveness.
Updated Dec 10, 2003
Why do I need to get vaccinated against the flu
every year?
Flu viruses change from year to year, which means two things. First, you can
get the flu more than once during your lifetime. The immunity (natural protection
that develops against a disease after a person has had that disease) that is
built up from having the flu caused by one virus strain doesn't always provide
protection when a new strain is circulating. Second, a vaccine made against
flu viruses circulating last year may not protect against the newer viruses.
That is why the influenza vaccine is updated to include current viruses every
year.
Another reason to get flu vaccine every year is that after
you get vaccinated, your immunity to the disease declines
over time and may be too low to provide protection after
one year.
Updated Dec 10, 2003
How are the viruses for flu vaccine selected?
Each year, many laboratories throughout the world, including in the United
States, collect flu viruses. Some of these flu viruses are sent to one of four
World Health Organization (WHO) reference laboratories, one of which is at
the Centers for Disease Control and Prevention (CDC) in Atlanta, for detailed
testing. These laboratories also test how well antibodies made to the current
vaccine react to the circulating virus and new flu viruses. This information,
along with information about flu activity, is summarized and presented to an
advisory committee of the U.S. Food and Drug Administration (FDA) and at a
WHO meeting. These meetings result in the selection of three viruses (two subtypes
of influenza A viruses and one influenza B virus) to go into flu vaccines for
the following fall and winter. Usually, one or two of the three virus strains
in the vaccine are changed each year.
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