Seasonal flu vaccines may protect individuals not only against the strains of flu they contain but also against many additional types, according to a new study.
Researchers at St Jude Children’s Research Hospital in US found that some study participants who reported receiving flu vaccines had a strong immune response not only against the seasonal H3N2 flu strain from 2010, when blood samples were collected for analysis, but also against flu subtypes never included in any vaccine formulation.
The finding is exciting because it suggests that the seasonal flu vaccine boosts antibody responses and may provide some measure of protection against a new pandemic strain that could emerge from the avian population, according to senior study author Paul G Thomas, an Associate Member in the Department of Immunology at St Jude.
Thomas and colleagues studied blood samples taken from 95 bird scientists attending the 2010 annual meeting of the American Ornithologist Union.
They exposed plasma from the samples to purified proteins of avian influenza virus H3, H4, H5, H6, H7, H8 and H12 subtypes using two laboratory tests to see how many different viruses participants reacted to, and how strongly.
The first test, ELISA, measures if any antibodies combine in any way to a protein called HA on the surface of the virus.
The second, HAI, measures if antibodies can bind to HA and interrupt its association with a substance viruses use to get inside human cells.
In the ELISA tests, 77 per cent of participants had detectable antibodies against avian influenza proteins.
Most individuals tested had a strong antibody response to the seasonal H3N2 human virus-derived H3 subtype, part of that year’s vaccine (2009-2010), but many also had strong measurable antibody responses to group 1 HA (avian H5, H6, H8, H12) and group 2 HA (avian H4, human H7) subtypes.
Sixty-six per cent of participants had some level of detectable antibodies against four or more HA proteins, and a few had responses to all subtypes tested, most of which have not previously been detected in the human population.
In additional experiments, the scientists found that participants who had significant antibody responses did not necessarily also have significant immune system T cell responses to avian viruses.
The study was published in mBio, the online open-access journal of the American Society for Microbiology.