Thousands of patients who visited a Sydney GP for vaccinations over almost a decade have been warned their immunisations may have been ineffective.

Key points: Patients of doctors Darrel and Brinda Weinman in Burwood have been contacted

Patients of doctors Darrel and Brinda Weinman in Burwood have been contacted It is unclear how many of those patients had the vaccines

It is unclear how many of those patients had the vaccines Health authorities say patients immunised there should be vaccinated again

Sydney Local Health District said vaccines at the Burwood practice at 40 Lindsay Street run by doctors Darrel and Brinda Weinman were incorrectly stored and some had expired.

Patients who received vaccinations since 2010 are being urged to contact a new GP and seek advice about being vaccinated again.

Sydney Local Health District's Clinical Director of Public Health, Dr Leena Gupta, said a range of vaccines on the National Immunisations Scheme, including the Measles Mumps and Rubella vaccine and Whopping Cough, were affected.

"We are writing to patients of that practice to ask them to get advice from a new GP on the need for re-vaccination," Dr Gupta said.

"While NSW Health does not have responsibility for GPs, we are assisting co-regulators the Medical Council of NSW and the NSW Health Care Complaints Commission in investigating and responding to these incidents."

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Inconsistent record keeping at the practice had made it difficult to obtain contact details for all patients and it was unclear how many have been affected, Dr Gupta said.

"There is no harm in giving a vaccine that is less effective, other than needing to be re-vaccinated again," Dr Gupta said.

"Re-vaccination in itself is unlikely to cause any harm."

Dr Brinda Weinman retired late last month and has been assisting with the investigation.

Dr Darrel Weinman passed away in October last year.

Dr Gupta said the practice was found to have not maintained its accreditation since 2010.

The practice did not administer the annual flu vaccine this year and did not store travel vaccines.

A total of 36 people in NSW have been diagnosed with the measles, a highly contagious viral disease, since January, compared to 19 cases last year.

Record numbers contracted the virus in Europe in 2018, according to the World Health Organisation, with more than 80,000 reported cases.

Patients who have not received a letter are advised to visit Sydney Local Health District's website at www.slhd.nsw.gov.au/publichealthnotices or phone 1800 959 939 for more information.