Should you bother getting a flu shot this fall? The last three flu seasons
have been pretty mild, and the vaccine can’t protect you entirely. But
as this ScienCentral News video reports, one scientist found out why skipping
a flu shot one year can increase your flu risk the next.
Nothing to Sneeze At
Every winter, some people, mainly those who are elderly or suffering from chronic
illnesses, die of influenza.
So every fall, health clinics, doctors' offices, and pharmacies offer flu
vaccinations. When one scientist got his recently, he also got some surprising
W. Deem, professor of bioengineering, physics, and astronomy at Rice
University in Houston, Texas, went to get his flu shot at a local pharmacy.
The nurse who vaccinated Deem mentioned that he ran some risk if he skipped
his flu shot the following year: “If I was getting the flu shot that
year, and not the year after, I might be more likely to get the flu the year
The nurse's warning startled Deem: shouldn't the effects of a flu vaccination
last for years, he wondered, the way vaccinations for polio or smallpox do?
He decided to look into what other researchers had found out about the immune
system and how it works. The nurse, he discovered, had been right: the risk
she mentioned is due to a biological phenomenon known as “original
antigenic sin”, first discovered in people and farm animals in 1953.
The term is a nod to both science and theology. An antigen
is biologists’ term for an invading organism, such as the influenza
sin is a theological concept that accounts for human flaws. Original antigenic
sin describes an apparent failing in the human immune system: it may recognize
a certain strain of a disease, such as this year’s strain of flu virus,
but then tries to combat an entirely different strain by "remembering"
how it fought the first strain it encountered. As a result, if you skip a
flu shot one year, Deem says, you may be more likely to get the flu during
that year, compared to your chances of illness if you had never gotten a flu
shot in previous years. "It’s as if the immune system didn't have
any memory whatsoever, and simply started to learn about this year's flu from
scratch," Deem says.
Three antibody fragments bind to the protein surface of influenza virus. image: Protein Data Bank, Rutgers University
When the human body is confronted with antigens, such
as flu virus or a vaccine,
it defends itself with antibodies—proteins
produced in white blood cells—that track down and fend off invading
antigens. A portion of each antibody containing just the right sequence latches
onto the part of an antigen with the exact matching sequence to form this
bond. Then the antibody either kills the antigen or signals other immune cells
Next time you are exposed to that particular antigen, you have antibodies that
usually protect you. But viruses that mutate as quickly as influenza does,
may have several different areas where antibodies could latch on—areas
that may change every year, foiling existing antibodies.
"The flu changes from year to year because of random mutations,"
says Deem. "When someone gets the flu, lymph nodes under the arms and
under the cheeks swell because they're producing different antibodies. Those
antibodies become better and better at recognizing the flu. Those antibodies
are still around the next year, and sometimes those antibodies don't respond
as well to a new flu as new antibodies would. So the immune system’s
memory actually inhibits the system from learning something new about the
flu next year."
At Rice, Deem and his research team developed a computational model that demonstrates
how original antigenic sin operates. "Our interest was in understanding
this phenomenon of original antigenic sin in a quantitative way," Deem
At present, to help combat new flu strains, every flu vaccine contains three
strains, and one
strain is changed annually. Deem hopes that with his model, “perhaps
we could point towards better design efforts for changing the flu vaccine
from year to year."
His research also could contribute to the development of vaccines for other
viral diseases to which original antigenic sin applies as well—HIV,
fever. Deem points out that their common feature is either multiple strains,
as in dengue fever, or very rapid mutation, as in HIV and the flu.
Meanwhile, he recommends a flu shot every fall: "The flu shot protects
you quite a bit against the flu this year, and your increased susceptibility
next year from original antigenic sin is much smaller than the increased protection
this year. And if you get the flu shot next year, you’ll be protected
against next year's flu.” Anyone who is particularly
susceptible should not skip an annual flu shot.