Pennsylvania: If you’re a person that gets a flu shot every year, chances are you have received it by now, along with the millions of others in the United States who have also been vaccinated. According to Centers for Disease Control survey data collected through early November 2016, forty percent of people have received a flu vaccine so far this year. Although getting the shot is simple enough, what goes into the vaccine, from a biological perspective to a policy point of view, is anything but. Flu vaccines work by priming the immune system with purified proteins from the outer layer of killed flu viruses. This induces immune cells to make antibodies that stop foreign invaders from infecting cells. Educating the immune system in this way readies it to attack flu viruses if the body sees them again.
Twice a year the World Health Organization (WHO) recommends viral
strains to put in vaccines for the Northern and Southern Hemisphere flu
seasons. Their last meeting was in September 2016. They chose the H3N2,
H1N1, and Flu B viral strains for the Southern Hemisphere vaccine, which
will be given as their winter season approaches in 2017. WHO will meet
next in February 2017 to choose the viral strains for the Northern
Hemisphere vaccine, which will be administered prior to our 2017-2018
winter flu season.
Basic research from the lab of Scott Hensley, PhD,
an associate professor of Microbiology, is changing how WHO makes their
decision about which viral strains will go in upcoming flu vaccines.
This has the potential to affect the health of millions of people
The Hensley lab studies viral evolution in real time. “Flu viruses
are constantly acquiring mutations in the proteins of their outer layer,
and many of these mutations prevent the binding of antibodies elicited
by prior influenza exposures,” Hensley said.
Complicating matters is “that all of us respond differently to the
flu vaccine, depending on our individual immune histories,” Hensley
said. “We now know that early childhood viral exposures impact how we
respond to flu vaccines and flu infections as adults.”
Hensley and colleagues discovered that these early childhood
“immunological imprints” affect how people respond to the current H1N1
vaccine. The vaccine being used in 2016 in the Northern Hemisphere
contains a weakened HINI flu strain from 2009.
For some people who are middle-aged now, born prior to 1985, their
first exposure to the flu was from an H1N1 virus that emerged in 1977.
This 1977 virus elicited long-lasting immune responses that were
beneficial during the 2009 H1N1 swine flu pandemic, since the 1977 and
2009 H1N1 viruses share some similarities. This meant that people who
were exposed to the 1977 strain were less likely to be affected by H1N1
in 2009. However, this benefit vanished in 2013 when H1N1 viruses
acquired a new mutation in a protein on its outer layer.
“This explains why middle-aged people were preferentially affected by the flu during the 2013-2014 season,” Hensley said. His lab showed that the new mutation in the H1N1 strain allowed viruses to avoid the immune response elicited in middle-aged adults.
They conducted tests against this outer layer protein using blood
drawn from 323 different-aged individuals prior to the 2013-2014 season.
that many middle-aged people produced antibodies that recognized the
H1N1 vaccine strain but failed to recognize the 2013-2014 circulating
H1N1 strain with the mutation. Individuals with these types of
antibodies were susceptible to the mutated 2013-14 H1N1 virus.
Initially, WHO did not recognize that the H1N1 virus circulating in
2013-2014 was distinct compared to the H1N1 vaccine strain. Part of the
reason for this oversight is because WHO relies on data from ferrets
never exposed to the flu virus to determine if new viral mutations are
important. In previous work, Hensley and colleagues found that ferrets
mount different antibody responses compared to most humans because
ferrets used for these studies live in captivity and have never been
exposed to flu viruses in the past.
According to WHO, upcoming flu vaccines will contain the updated H1N1
component so that the vaccine will work effectively in individuals of
These changes have already been made for the Southern Hemisphere
vaccine and should help for their upcoming flu season, says Hensley, but
for the Northern Hemisphere vaccine that most of us have already taken,
and does not contain the update, only time will tell regarding the
Perhaps by applying basic immunological research like that in the
Hensley lab, humans may be able to catch up a little to the rapid pace
of viral evolution.