A new preprint study examining more than 6,000 children has reported higher rates of several respiratory and infectious conditions among vaccinated children than among those who had received no vaccines before 13 months.
However, the researchers and outside experts stressed that the findings are observational and do not establish that vaccines caused the reported conditions, while calling for larger and more rigorous studies.
The study, conducted using medical records from eight paediatric practices, analysed 6,239 children, including 3,825 classified as unvaccinated. It compared children who received at least one vaccine before 13 months with those who received none during that period.
According to the study authors, vaccinated children had higher odds of recurrent respiratory disease, ear infections and strep throat.
They reported that children vaccinated before 13 months had 60 per cent higher odds of recurrent respiratory disease, 100 per cent higher odds of ear infection and 130 per cent higher odds of recurrent strep throat compared with the unvaccinated group.
The analysis also reported an apparent dose-response pattern for some conditions, with higher numbers of vaccine doses associated with higher odds of recurrent strep infections and rhinitis.
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Brian Hooker, chief scientific officer of Children’s Health Defense and a co-author, said the findings showed that “the risk increased in the vaccinated group based on increasing number of vaccines.”
The researchers also reported that developmental delay was not significantly associated with vaccination across the entire study population, although they found a higher association among children receiving larger numbers of doses.
Medical researcher Neil Z. Miller, who was not involved in the study, said the findings provide “important signals that warrant further investigation,” according to the study’s reporting organisation.
The researchers acknowledged that their sample was a convenience sample drawn from eight paediatric practices and that the analysis could not establish the timing of some health conditions in relation to individual vaccinations.
It also did not identify whether particular vaccines were responsible for any of the reported associations.
Miller noted that the research could not fully account for potential confounding factors, including gestational age and birth weight, and said larger studies using more robust methodology would be needed before firm conclusions could be drawn.
The study was also published as a preprint, meaning it has not yet undergone the full peer-review process normally required before publication in a scientific journal.
The authors themselves acknowledged the possibility of biases, including “survivor bias” and differences between families who vaccinate their children and those who do not.
The findings are likely to add to an ongoing debate over childhood vaccination schedules, particularly among researchers questioning whether existing studies adequately compare vaccinated and genuinely unvaccinated children.
Hooker argued that direct comparisons between the two groups remain relatively uncommon and called for further research into recurrent childhood infections.
However, the study’s results should not be interpreted as evidence that routine childhood vaccines are generally unsafe or that parents should abandon recommended immunisations. A single observational preprint cannot determine causation or outweigh the broader body of evidence on vaccine benefits and risks.
The study nevertheless highlights an area requiring further investigation: whether differences in vaccination status are associated with long-term patterns of childhood health, and how factors such as genetics, socioeconomic conditions, healthcare access and underlying health influence those outcomes