Pregnant women are the highest risk group to develop severe influenza illness and even can die from it. This disadvantage for maternal health has been observed during so-called pandemics, the last one known as Mexican or Swine flu in 2009. Here, women had a 5 times higher risk to be admitted to hospital, compared to non-pregnant women.The mechanisms underlying this increased influenza risk for pregnant women are still largely unknown. Therefore, we aim to understand whether the influenza virus may be altered when a pregnant individual is infected. We also want to understand how the maternal immune system during pregnancy responds to the influenza virus and compare this to the immune response of non-pregnant individuals.