A November 2023 Facebook post (archived here) features permanently banned Australian naturopath Barbara O’Neill talking about flu vaccines.

“They have taken mercury out of childhood vaccinations but they're still in the flu vaccines,” she says.

“... Because of the mercury in the flu vaccines, you ask any aged care nurse, when the flu shots go around Alzheimer's patients get worse, dementia patients get worse, people that didn't have Alzheimer's get it, some get the flu very badly, some die."

Ms O’Neill was speaking at an event at the Royal Oak Seventh-Day Adventist Church in Auckland in 2016.

Several additional videos featuring her can be seen on the church’s YouTube channel.

She refers to thiomersal, also often called thimerosal, which contains about 50 per cent mercury and is used as a preservative in some multi-dose vaccines in very small amounts to prevent bacterial growth.

However, it is no longer used as a vaccine ingredient in New Zealand or Australia.

Australia’s Department of Health and Aged Care states thiomersal was removed from all vaccines on the National Immunisation Program (NIP) more than two decades ago.

The National Centre for Immunisation Research and Surveillance (NCIRS) explains that it was removed as a precaution (See Page 2) to reduce "a theoretical risk" to small premature babies from repeated exposure to thiomersal-containing vaccine doses and to reduce the exposure of infants to overall environmental mercury where other sources such as in seafood are harder to eliminate.

In NZ, no vaccines on the Immunisation Schedule contain thiomersal either.

The Therapeutic Goods Administration (TGA), Australia’s vaccine regulator, confirmed in an email to AAP FactCheck that none of the NIP vaccines contain thiomersal, including seasonal influenza vaccines.

Professor Helen Petousis-Harris, a vaccinologist at the University of Auckland, said the move away from thiomersal in NZ began around the year 2000.

“Very few influenza vaccines contain thiomersal and none in NZ for many years,” Prof Petousis-Harris told AAP FactCheck in an email.

“One reason is because thiomersal is used as a preservative and this is not required in single dose vials.

“It is essential in multi-dose vials. In NZ we use almost exclusively single dose unless there is a pandemic or something.”

Prof Petousis-Harris confirmed the mRNA COVID-19 vaccines do not contain any thiomersal.

Ms O’Neill’s claim that mercury in vaccines causes Alzheimer’s disease to develop or worsen is also unfounded.

Australia’s National Centre for Immunisation Research and Surveillance states that “there is no evidence” that it causes any health problems except minor reactions, such as redness at the injection site.

A TGA representative says “no evidence” has been found linking it with Alzheimer’s disease or dementia, "either by causing the conditions or exacerbating them”.

Prof Petousis-Harris agreed.

The message is mirrored by the World Health Organization (WHO).

The WHO explains that thiomersal contains ethylmercury which is “very different” and considered far less toxic than methylmercury, often found in contaminated seafood and shellfish.

The American Centers for Disease Control and Prevention explains on its website that ethylmercury “is cleared from the human body more quickly than methylmercury, and is therefore less likely to cause any harm.”

AAP FactCheck has tackled other claims by Ms O’Neill here and here.