A new Stanford study debunked the long-held belief that pregnancy weakens immune responses.

Researchers from the School of Medicine and Lucille Packard Children’s Hospital found that pregnant women have a surprisingly strong immune response to influenza viruses, including H1N1. The study compared immune cells of pregnant and non-pregnant women and found that H1N1 causes pregnant women’s white blood cells to produce more molecules that attract other immune cells to an infected site.

“We now understand that severe influenza in pregnancy is a hyperinflammatory disease rather than a state of immunodeficiency,” said Catherine Blish, the study’s senior author.

Currently, influenza treatment for pregnant women involves drugs that slow down the replication of the flu virus in their bodies. Future studies, in conjunction with the new finding, may pave the way to new immune-modulating treatment approaches, said Alexander Kay, lead author for the study.

The study also raises the possibility that pregnant women’s immune responses to other viruses also strengthen.