A recent study from the Perelman School of Medicine at the University of Pennsylvania has revealed that older adults may have greater natural resistance to H5N1 avian influenza-commonly known as bird flu-compared to younger individuals and children. Published today in Nature Medicine, the research attributes this increased immunity to previous exposure to certain seasonal influenza viruses.

Dr. Scott Hensley, Professor of Microbiology and senior author of the study, explained, "Early childhood exposure to certain seasonal influenza strains appears to offer a lifetime immune response that partially protects against the H5N1 avian flu virus. While these antibodies might not completely prevent infection, they can significantly reduce disease severity."

H5N1 viruses, particularly the recent variant known as clade 2.3.4.4b, have primarily affected birds but have increasingly been found among mammals. Though currently ineffective at infecting human respiratory systems efficiently, mutations could allow easier human-to-human transmission, posing a pandemic risk.

Researchers analyzed blood samples from more than 150 participants born between 1927 and 2016. They discovered that those born before 1968, who had early-life exposure to seasonal flu strains such as H1N1 and H2N2, had elevated antibodies capable of binding to the H5N1 virus. Younger individuals lacked these protective antibodies.

Further research, including blood samples from participants who received a 2004 H5N1 vaccine, confirmed that older adults possessed higher initial antibody levels against H5N1, though vaccinations significantly boosted antibody responses in children and younger adults.

"Our results suggest that if an H5N1 pandemic emerges, children and younger adults would likely face higher risks," said Dr. Scott Hensley, senior author. "Thus, prioritizing younger age groups in vaccination programs could be essential."

The study was funded by the National Institute of Allergy and Infectious Diseases (NIAID).