Bankstown-Lidcombe Hospital, in Sydney’s south-west, has said some babies on site over the past few months may have been given an ineffective Hepatitis B vaccine.
The hospital has begun contacting around 300 mothers who gave birth between November 29 last year and January 22 this year to alert them to the potential problem.
The hospital said a fridge that stored the routine vaccines was found to have low temperature readings.
Three women who received a postnatal dose of whooping cough vaccine this month have also been contacted and offered a replacement dose.
The hospital has been plagued by several issues in recent years.
In July 2016 a problem with an oxygen supply outlet left one baby dead and another injured.
It followed an incident at the hospital in January 2014, in which another newborn baby was affected by a loss of oxygen.