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New Delhi, Feb 27: A recent study has found that previous infections with seasonal H1N1 flu may enhance immunity against the H5N1 bird flu, potentially reducing its severity in humans.
Published in the journal Emerging Infectious Diseases, the study provides insights into why most reported human cases of H5N1 in the United States have not resulted in fatalities. Researchers from the University of Pittsburgh and Emory University examined how pre-existing immunity influences infection severity.
Using a ferret model, the study revealed that animals previously exposed to H1N1 flu exhibited milder symptoms and lower mortality rates when later infected with H5N1. In contrast, those without prior immunity suffered severe illness and faced higher fatality rates.
“All human flu pandemics emerge in the context of pre-existing immunity,” said lead researcher Valerie Le Sage, assistant professor of microbiology and molecular genetics at the University of Pittsburgh. “Our model isn’t perfect, as the human immune response is more complex, but it’s crucial to study prior immunity’s role in pandemic risk assessment.”
Ferrets, which show flu symptoms similar to humans—such as fever, sneezing, and nasal congestion—provided key insights into immune responses. The study found that ferrets previously infected with H1N1 survived H5N1 exposure despite experiencing similar lung tissue damage. These animals exhibited lower fevers, reduced weight loss, and maintained higher activity levels compared to those without prior immunity. They also cleared the virus faster from their nasal passages, limiting the infection to the respiratory tract, whereas naïve ferrets (those without prior H1N1 immunity) displayed systemic infection, with the virus spreading to the heart, liver, and spleen.
The findings highlight the importance of considering pre-existing immunity in pandemic risk assessments and vaccine development strategies. The research suggests that past flu infections may offer some natural protection against emerging viral threats. As H5N1 continues to circulate in wild birds, poultry, and livestock, scientists emphasize the need for ongoing surveillance and preparedness efforts to mitigate potential outbreaks.
Disclaimer: This study is based on animal models, and its findings may not fully translate to human immunity. Further research is necessary to confirm its implications for public health and vaccine strategies.
