First flu infection key to immune protection; new coronavirus needs more than travel-related screening
Exposure to certain influenza viruses during childhood gives people partial protection for the rest of their lives against distantly related influenza viruses, according to a team of scientists at the University of California, Los Angeles (UCLA). The idea of “immunological imprinting,” where past exposure to the flu virus determines a person’s future response to infections, may explain why some people fare much worse than others when infected with the same strain of the flu virus.
In the new study, the scientists investigated two subtypes of influenza virus, H3N2 and H1N1, have been responsible for seasonal outbreaks of the flu over the past several decades. H3N2 causes the majority of severe cases in elderly people, and the majority of deaths from the flu; H1N1 is more likely to affect young and middle-aged adults, with fewer fatalities.
Data analysis revealed that those first exposed to the less severe strain, H1N1, during childhood were less likely to end up hospitalised if they encountered H1N1 again later in life than those who were first exposed to H3N2, who subsequently received extra protection against H3N2 later in life.
James Lloyd-Smith, a UCLA professor, explained that a first infection from one strain does confer some future protection from another, and the protection against future infections is much stronger when one is exposed to strains from the same group one has battled before.
However, despite earlier data showing that exposure to one cangrant considerable protection against the other, it also revealed a perplexing pattern: people whose first childhood exposure was to H2N2, a close cousin of H1N1, did not have a protective advantage when they later encountered H1N1.
Postdoctoral fellow at the University of Chicago, Katelyn Gostic, thus thinks the human immune system struggles to recognise/defend against closely related strains of seasonal flu, even though they are essentially the genetic sisters and brothers of past strains.
“We hope that by studying the broader immunity against bird flus and against seasonal flus – where our immune system seems to have bigger blind spots – we can uncover clues useful to universal influenza vaccine development.”
Meanwhile, the UCLA scientists report that screening travelers is not very effective for the 2019 coronavirus, and will only identify less than half of infected travelers, on average – most infected travelers have no symptoms yet, and are unaware that they have been exposed.
“This puts the onus on government officials and health officials to follow up with travelers after they arrive, to isolate them and trace their contacts if they get sick later,” said Lloyd-Smith.
Many governments have started to impose quarantines, or even travel bans, as they realise that screening is not sufficient to stop the spread of the coronavirus.
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