Influenza is a very common disease -- so common, in fact, that whenever we have the (classic) symptoms of fever, chills, headache, aches and pains, and "malaise" (the technical term for "feeling lousy") we tell ourselves and others that we have "the flu". This may be true, and often is true during the flu season (1-3 months during the winter), but you should bear in mind that there are many other viruses that can produce similar symptoms -- and a few bacteria as well.
After the initial "flu-like" symptoms, cough, congestion, and sore throat become worse in most cases; you may also have viral "pink eye" and/or abdominal symptoms (stomach ache, nausea, and vomiting). Muscle aches and pains can be bad enough to make walking difficult. Usually the symptoms subside within a week or so.
In small children, influenza can also cause bronchiolitis (inflammation of the small air passages of the lungs). The symptoms are similar to those seen with respiratory syncytial virus (RSV), and the treatment is similar. There are many other potential complications of influenza infection; one I see rather often during the season is temporary suppression of white blood cell production, which can make a child more susceptible to some bacterial infections.
There are three types of true influenza virus: A, B, and C. A and B are responsible for most of the flu epidemics we encounter. The A type can be divided into "strains" based on two antigens, the H and the N; every year or so at least one minor change occurs in either the H or N or both antigens, but that change is enough to make people who had the previously popular strain susceptible to the new one. Large changes in the antigen ("shift") of the A virus happen about every 10 years, and result in large epidemics, or pandemics, since most people aren't at all immune to the shifted virus. The most infamous flu pandemic was in 1918, near the end of the First World War: 20,000,000 people died of the flu -- more than were killed by World War I. The annual minor changes, or "drifts", may result in strains that lots of people are susceptible to, but this can take several years.
Each year the U.S. Centers for Disease
Control and Prevention (CDC) and vaccine manufacturers try to predict
which strains are most likely to cause flu epidemics for the next year,
and then produce vaccines tailored to those strains.
Because of the constant change in the flu virus, the vaccine needs to be
changed each year to protect against the flu strains that are expected to
be responsible for that year's flu infections -- and you need to get
the new vaccine each year to be protected against that year's expected
strains. The flu vaccine for a given season usually contains
antigens from three different strains, two A strains and one B strain.
For the 2007-2008 season, the strains are:
The A/Brisbane/10/2007 and B/Florida/4/2006 viruses are currently
circulating in the Southern Hemisphere.
A strain is named based on its type (A, B, or C), where it was first isolated
(it used to be country-based, but now isolations can be localized to
a particular city), the year of isolation, and the strain number -- the
A/Wisconsin strain for 2007-2008 was isolated in 2005), and the "serial
number" of the isolation for that year.
Influenza viruses actually infect wild and domestic birds,
swine, and other animals, which makes them almost impossible to eradicate --
especially since most birds, including wlid birds, can carry the viruses
without getting sick.
The "swine flu" of the mid-1970's was actually reported first in swine,
and millions of Chinese chickens were destroyed in late 1998 to help
control the possible spread of the Hong Kong flu strain to people. The
currently circulating "bird flus" has killed some poultry; only a
relatively few people have been infected with bird flu, and only about 100
people worldwide have died of it -- and all of them came in contact with
infected birds. No one has yet gotten bird flu from another person (at
least as of this writing.) We do not yet know if the bird flu virus could
mutate into something that could be passed from person to person.
For that matter, we haven't really seen a single antigen pattern to bird flu.
Most of the reported human infections were with an H5N1 flu virus, and the
H5N1 strain is the most common bird flu strain and is often referred to as
"the bird flu". There is now (as of April, 2007) a vaccine available for
an H5N1 flu virus strain: the vaccine is not available at the moment, because
it has been stockpiled by the US government for use in an emergency. However,
according to CDC, there have also been
confirmed "bird flu" cases invloving H7N2, H7N3, H7N7, and H9N2 flu viruses.
Since the vaccines have to be different for different strains, this could
be a problem in case of an epidemic if a flu virus spreads faster than we
can produce and distribute a vaccine against. Fortunately that hasn't
happened yet.
In the past we usually did not vaccinate every child routinely against flu.
However, because small children (between age 6 months and age 23 months)
are more likely to land in the hospital if they get the flu, we encourage
those children to receive the vaccine, and the
Advisory
Committee on Immunization Practices (which is responsible for
recommending immunizations in the US) recommends that every child
over age 6 months receive the flu vaccine. Until this year ACIP recommended
flu vaccination for all children up to age 5 years. On February 27, 2008,
the ACIP changed its recommendations and now recommends that every child
between 6 months and 18 years old receive the vaccine. The
recommendation is supposed to take effect no later than the beginning of
the 2009-2010 flu season, but it's possible that enough vaccine will be
available to vaccinate all children in the 2008-2009 season.
Some children are likely to have severe problems if they get the flu, and
they must be vaccinated every year. These include children with:
There are also some people who cannot receive the injectable flu vaccine.
The most frequent reason not to get the vaccine is allergy to eggs: the
vaccine viruses are "grown" on eggs, and some of the egg protein is still
present in the vaccine. Your doctor can and will review all the potential
reasons not to receive flu vaccine before giving it to you or your child.
The flu vaccine is usually given as a single dose. Children under 9
years old who are getting their first flu shot need two shots (4 weeks
apart if the injectable vaccine is used, 6 weeks apart for the
nasal-spray
vaccine. If a child does not receive 2 doses of flu vaccine the
first year he receives vaccine, he needs 2 doses the next year. After
that, only one shot is needed each year (although all of this may change
in a given year depending on the latest virus drifts and shifts).
It takes about a
month after the vaccine is given to develop full immunity. Side effects
usually include fever and aches and pains at the shot site. The outbreak
of Guillain-Barre syndrome associated with the 1976-77 "swine" flu vaccine
has not been seen again; Guillain-Barre is very rare among immunized people
and has not been firmly connected to flu shots in kids.
Unlike almost all viruses, there are
antiviral antibiotics
which can block "growth" (actually reproduction) of influenza viruses.
They are most helpful very early in a case of flu; once you have a
few million of the bugs in you the antivirals don't do much good.
There are four antiflu antivirals available at present. Two of
these -- amantidine and rimantadine -- prevent the
virus particles from taking off their outer coats (really!). Since
the virus can't infect a cell without shedding the outer coat, it
can't reproduce. These medicines work only on influenza A viruses.
The other two -- zanamivir and oseltamivir -- block an
enzyme called neuramidase (the N in the antigen code, by the
way)on the surface of the virus, which reduces the number of new
virus particles released by an infected cell. Since both influenza
A and influenza B have neuramidase on their surface (they have to,
to do their thing) both A and B can be blocked by zanamivir or
oseltamivir.
All of these medicines, when properly used within the first
48 hours of illness, will reduce the severity of flu inefction,
as well as how long you stay infected (by about 24 hours, but every
little bit helps). They will also lessen the chance that someone
else may get the flu from you. Three of these medicines (the odd
one out is zanamivir, which has to be inhaled -- the others are
pills or capsules that you swallow) have been shown to block
transmission of the flu from person to person. This would be very
helpful if we indeed run into a flu pandemic.
However, last year more than 90% of flu viruses checked by
CDC have been
resistant
to amantadine and rimantdine.
Why did this happen? I can think of two reasons:
For the 2008-2009 season, the strains will be:
Bird Flu
Who Should Receive Flu Vaccine?
Flu Antibiotics and Resistance
CDC recommended last year that
antiflu antivirals be used to prevent flu only by certain groups
of people who were not vaccinated until after an outbreak of
flu began in their area. These include:
Some vaccines, including some of the available flu vaccines, contain thimerosal, a preservative used in many vaccines and other medicines (including contact-lens storage and cleaning solutions) to prevent bacteria from growing in the solutions. Until a few years ago, many vaccines contained thimerosal, but it has been removed from almost all of the vaccines we now give to children. The only widely-used vaccine that still contains thimerosal is the flu vaccine, and only some manufacturers still produce flu vaccine that contains thimerosal.
Thimerosal is a mercury-based chemical. There is a theoretical risk of mercury poisoning from the thimerosal used to preserve vaccines. Although several researchers claim that there is evidence of such poisoning, and in particular an increased risk of autism with thimerosal-containing vaccines, this has not been well-proven, and several large studies in different countries show no change in the occurence of autism or other neurodevelopmental disorders between children given thimerosal-containing and thimerosal-free vaccines. A study by California public-health authorities published in the January, 2008 issue of the Archives of General Psychiatry and quoted in the New York Times, found that the autism rate in children rose steadily from 1995 to 2007 even though thimerosal was removed from all vaccines, except for some flu vaccines, in 2001. If thimerosal was in fact responsible for autism, autism rates should have fallen after 2004. They didn't.
Influenza infection is dangerous to infants. However, only two of the three flu vaccines on the market are meant to be given to children under age 2 years, and those vaccines are not recommended for children younger than six months. Therefore, most public health authorities, including the CDC, recommend that infants at risk receive flu vaccine starting at age 6 months whether or not the vaccine contains thimerosal. Some of the current vaccine is made with a reduced amount of thimerosal, reducing the theoretical risk of mercury poisoning, and that vaccine should be used for vaccinating children under age 3 years.
I am aware that there are many people who believe that thimerosal should
not be used to preserve vaccines. I believe that thimerosal
should not be used to preserve vaccines if at all possible. I also
know several people with autism and Asperger's syndrome, including one
in my own family. However, I also believe that flu is sufficiently
dangerous to patients, especially the very young (many of whom I admit
to the hospital every year with complications of flu), that any risk
from the preservative is MUCH less than that from influenza itself, and
I would not hesitate to vaccinate my family against the flu even if I
could not obtain preservative-free vaccine. (That is my opinion. Other
people's opinions differ. Some people have also pointed out that, if there
is a flu pandemic, any vaccine that is produced for the emergency
will have to have thimerosal as a preservative, since there won't be time
to produce single-dose vials of preservative-free vaccine. As always,
you need to talk to your own or your child'd doctor to help decide if
you or your child should receive the vaccine.)
The Nasal-Spray Flu Vaccine
We now have available a flu vaccine that can be sprayed into a patient's nose, rather than being given by injection. Flu-Mist®, or "live, attenuated, intranasal vaccine" (or "LAIV") is a solution of flu virus particles that are still alive but have been weakened and that grow best at temperatures way below that of the human body. Although the virus is alive, it is so weak that it will produce few, if any, symptoms in healthy people.
LAIV has been approved by the Food and
Drug Administration for use in people age 2 years to 49 years. (The
expansion to children 2-5 years old is new this season.) For
several reasons, including the possibility of flu symptoms appearing,
LAIV is not approved for use in children under 2 years, adults
50 or older, people with chronic diseases (like the ones listed above),
or children receiving aspirin; these people have to receive the injectable
vaccine. As with the injectable vaccine, a child less than 9 years old
needs 2 doses of the vaccine for full immunity in the first year she
receives the vaccine (or 2 doses in the second year of vaccination if
she only received one dose the first year), but the two doses of LAIV
must be given 6 weeks apart rather than the 4 week separation for the
injectable vaccine.
The injectable flu vaccine contains split particles of the flu virus, which
can induce immunity but can't actually make you sick. However, the virus
stock has to be grown before vaccine can be made from it, and growing the
virus takes a lot of time. The CDC has to
figure out what flu virus strains are needed for a given flu season 6-9
months before the season starts so that the manufacturers have enough time
to produce vaccine.
There were many problems with flu vaccine supply in the last 3-4 years,
resulting in real and practical shortages of flu vaccines in many areas.
Last year was supposed to be different. There are now four compainies
licensed by FDA to produce flu vaccine for use in the United States, and
there were as many as 115 million doses of vaccine available. The problem
with flu vaccine was in the distribution process: places like Wal-Mart
received their supplies on time, while many doctors and hospitals had to
wait for their shipments. Hopefully, distribution this year will run
more smoothly. If
anything, we may end up with some left over at the end of the season --
that can be expensive in other ways, but anyone who needs flu vaccine
will be able to find it, as will anyone not on the high-priority list
(people at high risk for flu-related problems, and those of us who take
care of or live with those people).
For more information on influenza, see the
CDC Web site.
See the Detailed Search
page for complete instructions on searching the Office. Supplies of Flu Vaccine
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Written 09/02/96; last revised 10/20/08