Daijiworld Media Network – New Delhi

New Delhi, Feb 27: A recent study suggests that prior infections with seasonal H1N1 flu may strengthen immunity against H5N1 bird flu, potentially reducing its severity in humans.

Published in the journal Emerging Infectious Diseases, the study sheds light on why most reported human cases of H5N1 in the US have not resulted in fatalities. Researchers from the University of Pittsburgh and Emory University explored how pre-existing immunity influences the severity of infection.

Using a ferret model, the study found that animals previously exposed to H1N1 flu experienced milder symptoms and lower mortality rates when infected with H5N1. However, those without prior immunity suffered severe illness and 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 exhibit flu symptoms similar to humans—such as fever, sneezing, and nasal congestion—provided key insights into the immune response. The study revealed that ferrets previously infected with H1N1 survived H5N1 exposure despite similar lung tissue damage. They exhibited lower fevers, reduced weight loss, and maintained higher activity levels compared to those without prior immunity. They cleared the virus faster from their nasal passages, restricting the infection to the respiratory tract, while naïve ferrets (without prior H1N1 immunity) displayed systemic infection, with the virus spreading to the heart, liver, and spleen.

The study underscores the need to consider pre-existing immunity in pandemic risk assessments and vaccine strategies. It also suggests that past flu infections may provide some natural defense against emerging viral threats. As H5N1 continues to circulate in wild birds, poultry, and livestock, researchers stress the importance of ongoing surveillance and preparedness efforts to mitigate potential outbreaks.