Dr Judy Mikovits, a discredited former virologist who has been debunked multiple times, made the claim in an interview on the often fact-checked One America News Network channel.

"They injected H5N1 in every flu vaccine since 2012, since 2009 actually," Dr Mikovits said (video mark six minutes, 20 seconds).

She shared the claim in posts on X, formerly Twitter, and Instagram, and users have also posted clips on Facebook. 

However, experts say the claim is false.

Seasonal flu vaccines in Australia do not contain the H5N1 virus strain. 

Australian vaccines contain four inactive influenza virus strains: two influenza A subtypes, H1N1 and H3N2, and two influenza B lineages, B Victoria and B Yamagata.

Tin Fei Sim, a pharmacist and an associate professor at Curtin Medical School, said no ordinary flu vaccines contain H5N1.

“There are eight seasonal influenza vaccines registered in Australia this year, and none of them contain H5N1 or H5N1-like virus strain,” she told AAP FactCheck.

The ingredients for the eight jabs and other, non-seasonal flu jabs have been published on the website of Australia’s drug regulator, the Therapeutic Goods Administration. 

H5N1 is not listed as an ingredient in any of them.

American experts said Dr Mikovit’s claim was also wrong in relation to US seasonal flu vaccines.

Stephen S. Morse, an epidemiology professor at Columbia University in New York, said it wasn't clear what Dr Mikovits meant by H5N1 being “injected” into vaccines, but it was “fair to deem this misinformation”.

He said it would not make sense to put the H5N1 virus, which can cause fatal infections in humans, in the estimated 175 million seasonal flu jab doses distributed in the US each year.

“If there were actual H5N1 virus in the vaccine, there would be so many cases that it would be catastrophic, and very evident,” Prof Morse told AAP FactCheck.

Suresh K. Mittal, a distinguished professor of virology at Indiana's Purdue University, said US seasonal flu jabs “do not contain the H5N1 virus or any of its parts”.

Experts said the only type of flu vaccines that contained H5N1 were bird flu jabs.

The US has approved three human H5N1 vaccines, but none were commercially available at the time of writing. 

“The only current human H5N1 vaccine campaign I know of is the recently started effort to immunize animal workers in Finland because of their heightened risk of exposure,” Prof Morse told AAP FactCheck. 

“There simply isn’t enough H5N1 human vaccine to go around.”

The World Health Organization (WHO), a UN agency responsible for global health care and coordination, said almost all human cases of H5N1 had been linked to close contact with infected birds or contaminated environments such as live bird markets. 

Dr Mikovits has previously falsely claimed HIV does not cause AIDS, COVID is activated by face masks and flu vaccines increase the chance of getting COVID. 

Her H5N1 claim has particular similarities to other conspiracies she has promoted about secret vaccine ingredients, including that COVID-19 has been in polio jabs since 2004.