Pregnant Women At Greatest Risk Of Flu Due To Hyperactive (Not Weakened) Immune Systems

For the past however long, mums-to-be have suffered from the flu virus worse than any other member of the public due to (what was believed to be) a weakened immune system.

However, a new health study has found that this isn't actually the case.

The immune systems of pregnant women are, in fact, hyperactive - an unexpected discovery as immune responses are thought to be suppressed by pregnancy in order to prevent a woman's body from rejecting her unborn baby.

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."

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.

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.

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

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 reported 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 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," Dr Kay said. "But only 50% of pregnant women are currently vaccinated for influenza."