Monica Smit, who AAP FactCheck has debunked several times, made the claim in a social media video posted on July 18. 

“... vaccines are the third leading cause of death in children in third world countries,” she said.

In the comments section, a user asked: “Are you referring to covid vaccinations causing death in these poor children? Or covid?” and Ms Smit replied: “no just jabs in general”.

AAP FactCheck contacted Ms Smit for her evidence but did not receive a response.

It’s unclear what Ms Smit defines as a “third-world country”, but AAP FactCheck has taken this to mean developing countries, of which the Australian government has published a list as declared by the foreign affairs minister.

Associate Professor Li Liu is a population health researcher at Johns Hopkins University and co-principal investigator of the child and adolescent causes of death estimation project. 

She works alongside the United Nations Inter-agency Group of Child Mortality Estimation to compile a dataset on child deaths, with the latest figures for 2021.

Dr Liu said causes of death included in the data are based on the international classification of diseases, by the burden of disease and amount of data available.

She told AAP FactCheck the three leading causes of death in children under five globally are prematurity, lower respiratory infections or pneumonia, and birth asphyxia or trauma.

The UN data shows these are also the three leading causes of under-five deaths across developing countries.

Dr Liu added that “many deaths due to lower respiratory infections can be effectively prevented by vaccines, such as Hib and Pneumococcal”.

The "other" category covers various causes of death that aren't specifically singled out in the UN dataset, including "all other communicable, maternal, perinatal, nutritional, and non-communicable diseases".

Statistics for child deaths generally refer to children as those under five years, because this age group can be used as a proxy for overall child health.

In countries with high child mortality rates, a large proportion of these deaths occur before age five. 

World Health Organization spokesman Paul Garwood told AAP FactCheck the claim in the video was “inaccurate and false”.

“The exact opposite of what was stated is true," he said. "It is the absence of vaccines that poses great health risks to children worldwide, especially in low-income settings."

He confirmed the leading causes of death in children under five are preterm birth complications, birth asphyxia or trauma and pneumonia, along with congenital anomalies, diarrhoea and malaria.

He explained all of these “can be prevented or treated with access to simple, affordable interventions including immunization, adequate nutrition, safe water and food and quality care by a trained health provider when needed".

UN data published in 2023 shows 57 per cent of under-five deaths occur in sub-Saharan Africa, while southern Asia accounted for 26 per cent of under-five deaths (page 7). 

Mr Garwood said the leading cause of death differs between regions over time. 

“For instance, malaria is still a leading cause of under-five deaths in sub-Saharan Africa, accounting for about 15 per cent of all deaths in the region whereas it accounts for just 0.1 per cent of under-five deaths in Southern Asia (figure 5, page 24).

“And in Southern Asia … the cause-of-death distribution is dominated by cases related to complications around the time of birth - for instance, one in four under-five deaths in this region is due to prematurity.”

AAP FactCheck has also previously checked comments made by the group Ms Smit founded, Reignite Democracy Australia.