"Pregnant women are at particularly high risk of severe complications and death from influenza because of the changes that occur to their immune and other systems during pregnancy," New Zealand College of Midwives spokesperson Lesley Dixon said.
Immunisation during pregnancy also gives protection for the baby's first few months of life outside its mother.
Plunket clinical advisory manager Karen Magrath said babies less than six months were too young to be immunised but if their mothers were vaccinated they could pass protection on to the baby.
All pregnant women are entitled to a free vaccination until the end of July.
Those who are also eligible include people aged 65 and over, and anyone with serious long-term conditions, and children aged from 6 months to 5 years who have been hospitalised for respiratory illness.
DHB Medical Officer of Health Nicholas Jones said the vaccine was "generally well tolerated" and it was a myth influenza could result from the jab. Most reactions were mild.
"That's entirely preferable to a serious illness which can have severe effects, including hospitalisation, complications and even death."
Every year influenza kills about 400 New Zealanders and more than 1000 are admitted to hospital.
