Last year was a lousy year for the
flu vaccine. Hospitalizations for flu hit a nine-year high, and the vaccine
prevented flu in only 23% of all recipients, compared with 50% to 60% of
recipients in prior years.
Why does the flu vaccine work well
in some winters and not others? The flu vaccine primes the immune system to
attack two proteins on the surface of the influenza A virus, hemagglutinin (H)
and neuraminidase (N). Different flu strains have different combinations of
these proteins — for example, the strains targeted by recent flu vaccines are
H3N2 and H1N1.
Unfortunately, the influenza virus
is microbiology’s answer to Miley Cyrus: it can change enough in just one year
to become completely unrecognizable. The H and N proteins are genetic
chameleons that undergo constant transformation. This process is called antigenic
drift, and it regularly flummoxes vaccine makers, public health experts,
and your immune system.
Developing
the new flu vaccines
Most flu vaccine in the United
States is made from chicken eggs, using production methods that date back to
1945. This cumbersome technique requires 6-8 months of lead time to produce
enough vaccine for the upcoming flu season. Every February, the World Health
Organization and the Food and Drug Administration (FDA) make their best guess
as to which flu strains should be covered by next winter’s vaccine, based on a
review of circulating flu viruses from over 100 countries. But a lot can change
in 8 months, especially with influenza. This past year, the “drifted” H3N2
influenza strain didn’t match up with the vaccine strain, explaining the
vaccine’s poor performance.
Can researchers build a better flu
vaccine? They probably already have. The FDA has approved two alternatives to
traditional egg-based vaccines. One of these, Flucelvax, uses influenza virus
grown in kidney cells that were originally obtained from a single cocker
spaniel in 1958. The other one, FluBlok, is made by tricking insect cells into
pumping out large amounts of hemagglutinin, which is then purified and used in
the vaccine. These methods might sound outlandish, but they seem to be safe and
effective.
These newer vaccines have
several advantages:
They are safe for patients with egg
allergies. Because most flu vaccine is made
from eggs, many people with egg allergies can’t receive the traditional flu
shot.
They don’t require a massive supply
of chicken eggs, and could still be made even if a
bird flu epidemic wiped out chicken flocks.
They need less manufacturing time
than egg-based vaccines, meaning
vaccine production could be ramped up quickly in case of a flu pandemic. This
also might give the FDA more time to make their decision on which flu strains
should go into the vaccine, reducing the risk of a vaccine–flu mismatch like
last year’s.
Scientists are also working on a
universal flu vaccine, one that might not need to be changed every year. This
vaccine takes advantage of the fact that the H protein has two parts: a head
region, which is the part that changes rapidly, and a stem region, which stays
more or less the same. Small studies of vaccines using chunks of the stem have
shown promising results in animals. Trials of these vaccines are just beginning
in humans.
How the
flu vaccine reduces your risk
The CDC recommends that all American
adults get a flu vaccine every year. Even though the current vaccine is not
perfect, there are many good reasons for you to get it. The vaccine does reduce
your chance of getting the flu, especially when it matches up well with
dominant flu strains.
The benefits of flu vaccine are
particularly impressive in older adults. If you are 65 or older, it One reason
for this lowered risk is that getting the flu increases your risk of developing
bacterial pneumonia, which is responsible for many hospitalizations and deaths.
But this is not the only reason.
Inflammation is bad for your body,
and increases your risk of heart attack or stroke. If you’ve ever had
full-blown flu, and you remember how feverish, achy, and miserable you felt,
you know that influenza is great at filling your body with inflammation. So, as
you might expect, another benefit of the flu vaccine is that
Most adults, including me, receive
the flu shot made from chicken eggs. If you have an egg allergy, you should get
Flucelvak or FluBlok instead. If you are between ages 2 and 49, you are
eligible for the intranasal vaccine, which is inhaled rather than injected.
Because this vaccine contains live virus, it should be avoided if you are
pregnant, have a weak immune system, or are around other people with weak
immune systems. The intranasal vaccine may also cause wheezing, so you should
avoid it if you are asthmatic.
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