Study Suggests Younger Individuals May Benefit More from H5N1 Vaccination
New Delhi: A new study suggests that younger adults and children could gain greater benefits from H5N1 vaccines, even if the vaccines are not specifically designed for the current strain affecting birds and cattle.
Researchers from the University of Pennsylvania in the US found that previous exposure to certain seasonal influenza viruses helps the immune system develop cross-reactive immunity against the H5N1 avian influenza virus.
The study, published in Nature Medicine, revealed that older adults who had encountered seasonal flu viruses before 1968 were more likely to have antibodies capable of binding 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 university.
"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 been circulating in birds for years, but a newer strain—clade 2.3.4.4b H5N1—has emerged more recently and spread among cattle. This current strain does not efficiently bind to receptors in the human upper airway, but continued circulation among mammals could lead to mutations that enable it to infect human airway cells more easily and enhance transmission.
If such mutations occur, H5N1 could begin spreading from human to human. Current flu vaccines mainly stimulate the production of antibodies that recognize hemagglutinin proteins, preventing the virus from infecting human cells.
For the study, researchers analysed blood samples from more than 150 individuals born between 1927 and 2016 to measure antibodies targeting the stalk proteins of various influenza viruses, including H5N1. They discovered that older adults born before 1968—who were likely first exposed to H1N1 or H2N2 in childhood—had higher levels of antibodies capable of binding to the stalk of the H5N1 virus.
The findings indicated a strong link between an individual’s birth year and the levels of H5N1-fighting antibodies in their blood. Young children who had not encountered seasonal flu viruses had lower levels of these protective antibodies.
Hensley emphasized that in the event of an H5N1 pandemic, all age groups would likely be highly susceptible. However, the disease burden might be highest in children. "If this is the case, children should be prioritised for H5N1 vaccinations," he stated.