Healthy young adults may be vulnerable to viruses such as swine flu because their immune systems over-react, according to a new analysis published last night.
Doctors in Tennessee, USA – who treated several critically ill young adults during the outbreak – say they have found scientific evidence to support their theory.
Their findings were published last night in the journal Nature Medicine.
Their research took them to Argentina and by studying tissue samples of flu epidemic victims over decades they confirmed many victims had high levels of an antibody called C4d.
These included victims of the 1957 Hong Kong flu pandemic in Nashville, Tennessee.
Researcher Dr John Williams, of Vanderbilt University Medical Center, Nashville, said: "C4d is part of the inflammatory cascade, and while it’s really good at killing organisms and protecting us, it’s sort of the slash and burn approach, capable of causing lots of tissue damage."
Fellow researcher Professor Fernando Polack said: "We found in 2009, the elderly had good immunity because they had seen a very similar virus sometime before 1957. Babies hadn’t seen many viruses at all so there was no trigger. It came down to the young adults – primed with an ineffective response.
"Their bodies already had defences against previous influenza viruses that look like this one but weren’t close enough.
"It suggests this (immune over-reaction) is what happens with pandemic to make young healthy adults seriously ill. There are other things that contribute to threat, but this is one of the main things for this age group."
Nature Medicine December 5 2010
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