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Childhood influenza exposure subtype predicts future immunity
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Childhood exposure to influenza can determine which avian influenza strains a patient will be immune to in the future, study data show. The researchers also reported that birth year could be predictive of how likely a patient would be to die or become seriously ill in the event of an animal-origin flu epidemic, explaining why influenza pandemics tend to have different impacts on specific age groups.
“These findings challenge the current paradigm, where the entire population would be immunologically defenseless in a pandemic caused by a novel influenza virus,” Katelyn M. Gostic, doctoral student in the department of ecology and evolutionary biology at the University of California, Los Angeles, said in a press release. “Our results suggest it should be possible to forecast age distributions of severe infection in future pandemics, and to predict the potential for novel influenza viruses from different genetic groups to cause major outbreaks in the human population.”
Researchers analyzed data from every known human case of the H5N1 and H7N9 influenza A viruses, reviewing more than 1,400 cases in total. Because the human immune system creates antibodies that target viral receptor proteins called hemagglutinins when a patient is first infected, a patient exposed to a certain hemagglutinin subtype will have a lower chance of becoming seriously ill from other viruses with similar hemagglutinins in the future, according Gostic and colleagues. All 18 known influenza A hemagglutinin subtypes fall into two main groups.
In an accompanying press release, Gostic and colleagues used the analogy of lollipops to explain why different age groups may be better equipped to cope with different influenza subtypes.
“Let’s say you were first exposed to a human ‘orange lollipop’ flu as a kid,” said Michael Worobey, DPhil, professor of ecology and evolutionary biology at the University of Arizona. “If later in life you encounter another subtype of flu virus, one from a bird and one that your immune system has never seen before but whose proteins also are of a similar ‘orange’ flavor, your chances of dying are quite low because of cross-protection. But if you were first infected with a virus from the ‘blue lollipop’ group as a kid, that won’t protect you against this novel, ‘orange’ strain.”
The researchers noted that H7N9 tended to effect older adults, while H5N1 impacted children and young adults. They reported that the dividing line was 1968, the year of the Hong Kong flu pandemic. Patients born during or after 1968 were less likely to be infected with H7N9, which was closely related to the 1968 virus, while those born before the 1968 pandemic were more likely to be immune to H5N1.
“Our findings show clearly that this ‘childhood imprinting’ gives strong protection against severe infection or death from two major strains of avian influenza,” James Lloyd-Smith, PhD, associate professor in the department of ecology and evolutionary biology at UCLA, said in the press release. – by Andy Polhamus
Disclosures: The researchers report no relevant financial disclosures.
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