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Flu risk during pregnancy linked to 'hyperactive immune system'

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Pregnant women are worse hit by flu than other members of the population because their immune systems are hyperactive rather than weakened, a study has shown.

The discovery is unexpected since immune responses are thought to be suppressed by pregnancy to prevent a woman’s body rejecting her unborn baby.

“Severe influenza in pregnancy is a hyper-inflammatory disease rather than a state of immunodeficiency”

Catherine Blish

Researcher Dr Catherine Blish, from Stanford University in the US, said: “We were surprised by the overall finding.

“We now understand that severe influenza in pregnancy is a hyper-inflammatory disease rather than a state of immunodeficiency.

“This means that treatment of flu in pregnancy might have more to do with modulating the immune response than worrying about viral replication,” she said.

The researchers took immune cells from 21 pregnant and 29 healthy, non-pregnant women and exposed them to different flu viruses in the laboratory.

Cells taken from women six weeks after they had given birth were also tested.

Stanford University

Catherine Blish

Pregnancy boosted the immune response to swine flu, the H1N1 strain that caused a pandemic in 2009, by affecting two types of white blood cell, natural killer (NK) and T-cells.

Compared with those from non-pregnant women, both cell types produced larger amounts of signalling molecules that attract other immune cells to infection sites.

This could lead to lungs becoming clogged up by an influx of immune cells, said Dr Blish.

Catching flu when pregnant, especially pandemic strains, is known to heighten the potentially fatal risk of pneumonia.

“It opens the possibility that we can develop new immune-modulating treatment approaches in the setting of severe influenza”

Alexander Kay

Both swine flu and the seasonal flu strain H3N2 also caused NK and T-cells to be activated in a greater variety of ways in pregnant women, the researchers said in the journal Proceedings of the National Academy of Sciences.

Lead author Dr Alexander Kay, also from Stanford University, said: “If our finding ends up bearing out in future studies, it opens the possibility that we can develop new immune-modulating treatment approaches in the setting of severe influenza, especially in pregnant women.”

He said he hoped the research would remind women who are pregnant or planning a pregnancy to get their flu shots.

“Flu vaccination is very important to avoid this inflammatory response we’re seeing,” said Dr Kay. “But only 50% of pregnant women are currently vaccinated for influenza.”

 

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Readers' comments (2)

  • michael stone

    'We now understand that severe influenza in pregnancy is a hyper-inflammatory disease rather than a state of immunodeficiency.'

    I thought it was the current wisdom, that a lot of serious flu cases - especially in 'the young and previously healthy' - are hyper-inflammatory disease: isn't that the 'theory' for why the 1918/19 pandemic, seemed to kill so many young people ?

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  • This is interesting. The current flu vaccination causes side effects that inhibit maternity services staff from having the vaccine.
    We have been told that pregnancy lowers resistance due to suppressed immune system and also that pregnant women are not old enough to have come across all the strains, like in 1918.
    I would welcome any change from the current flu vaccine programme.

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