New Delhi, March 15 Younger adults and children would benefit more from H5N1 vaccines, even those not tailored specifically to the current strain circulating in birds and cattle, finds a study.
Researchers from the University of Pennsylvania in the US showed that prior exposures to specific types of seasonal influenza viruses promote cross-reactive immunity against the H5N1 avian influenza virus.
In the study, published in the journal Nature Medicine¸ older adults who were exposed to seasonal flu viruses that circulated before 1968 were found to be more likely to have antibodies that bind to the H5N1 avian flu virus.
“We know that early childhood influenza exposures can elicit immune responses that last a lifetime,” said Scott Hensley, Professor of Microbiology at the varsity.
“We found that antibody responses that were primed by H1N1 and H3N2 viruses decades ago can cross-react to H5N1 avian viruses circulating today. Most of these cross-reactive antibodies cannot prevent infections, but they will likely limit disease if we have an H5N1 pandemic," he added.
H5N1 viruses have circulated in birds for many years, but a new version -- clade 2.3.4.4b H5N1 virus -- emerged more recently and has since spread among cattle. This current H5N1 strain does not bind well to receptors in the human upper airway, but widespread circulation in mammals could lead to mutations that help the virus infect human airway cells and increase transmission.
If this occurs, H5N1 could potentially start spreading from human to human. Current influenza vaccines primarily elicit antibodies that recognise hemagglutinin proteins and prevent them from infecting a person’s cells.
The team tested blood samples from over 150 people born between 1927 and 2016 for antibodies targeting the stalk proteins of different influenza viruses, including H5N1. They found that blood samples from older adults born before 1968 who were likely first exposed to H1N1 or H2N2 in childhood had higher levels of antibodies that could bind to the stalk of the H5N1 virus.
They found that an individual’s birth year was closely linked to the amount of H5N1-fighting antibodies in their blood. Young children who were not exposed to seasonal flu viruses possessed low levels of antibodies that could fight H5N1.
Hensley said that in cases of an H5N1 pandemic, all age groups will likely be highly susceptible. But, the highest disease burden may be in children. “If this is the case, children should be prioritised for H5N1 vaccinations,” the expert said.
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