The NSW Health department has launched an investigation into a western Sydney hospital where several babies were given a potentially ineffective vaccine.
Bankstown-Lidcombe Hospital is in the process of contacting 282 mothers after a fridge that stored routine hepatitis B vaccines was discovered with low temperature readings.
The mishap is the latest bungle for the hospital which was responsible for the fatal gassing mix-up of two newborns last year which left one dead and the other disabled.
NSW Health on Tuesday confirmed a formal investigation into the latest incident was underway.
"The Local Health District is ... undertaking a formal investigation to determine how and why the breach occurred and outline measures to prevent any recurrence," the organisation said in a statement.
The investigation will involve representatives from both Health Protection NSW and the independent National Centre for Immunisation Research.
Mothers who gave birth at the hospital between November 29 and January 22 this year are being contacted but the hospital says for most no action will be needed - apart from ensuring their infant receives their remaining vaccines on time.
An additional vaccine will be arranged for 15 babies.
Mothers are advised that receiving the potentially less-effective vaccine wouldn't have been harmful.
"However some babies may not have received important early protection against hepatitis B," South Western Sydney Local Health District acting director of population health Dr Stephen Conaty said on Monday evening.
Labor has blasted the government over the incident and demanded new Health Minister Brad Hazzard guarantee the safety of the babies.
Mr Hazzard has refused to comment with his office referring media inquiries to NSW Health.
Dr Conaty says Hepatitis B infection in babies is rare in Australia.