Health and Human Services Secretary Robert F. Kennedy Jr. has consistently called for comprehensive long-term cohort studies comparing vaccinated and unvaccinated individuals to investigate potential links between vaccines—especially those containing aluminum—and autism or other health issues. However, Denmark has already conducted studies of equivalent or even greater scale over several decades, utilizing its national registry system to provide clear and robust answers. These findings systematically refute any credible association between vaccines and autism.
Denmark’s Epidemiological Strength: The Civil Registration System
Denmark’s success in this research is not due to experimental wizardry, but rather its robust infrastructure. Established in 1968, the Danish Civil Registration System (CRS) assigns every resident a unique ten-digit identification number. This number facilitates seamless linkage across nationwide health and administrative registers, ensuring nearly total coverage and follow-up on birth, vaccination, diagnoses, migration, and death. This system serves as the backbone of high-quality epidemiological research.
Landmark Study 1: Madsen et al. (2002) – MMR and Autism
In one of the earliest and most frequently cited studies, Madsen et al. (2002) utilized Denmark’s registries to track every child born between 1991 and 1998. Their analysis found no link between the MMR (measles-mumps-rubella) vaccine and the development of autism. This conclusion was quickly reinforced by medical commentary, adding to the study’s credibility.
Landmark Study 2: Hviid et al. (2019) – A Larger Scale, Still No Link
More recently, Hviid et al. (2019) expanded previous research by analyzing data from a staggering 657,461 Danish children born between 1999 and 2010. They considered familial risk factors, the impact of other vaccines, and the timing of autism diagnoses, ultimately finding no increased risk associated with MMR vaccination. Their findings persisted across subgroups, including children with a higher risk of autism, and examined diagnosis timing relative to vaccination.
Thimerosal, Aluminum, and Autism: No Connection
- Thimerosal (Mercury-Based Preservative)**: In 1992, Denmark removed thimerosal from its childhood vaccine schedule. If thimerosal had been a causal factor for autism, rates would be expected to drop; however, they continued to rise, disproving any such connection. Further analysis of nearly half a million Danish children confirmed no dose-response relationship with autism.
- Aluminum (Adjuvant)**: A 2025 Danish study involving 1.2 million children over more than two decades examined 50 health conditions—including autism, allergies, and autoimmune disorders—and found no association with aluminum-containing vaccines. Despite Robert F. Kennedy Jr.’s request for the study’s retraction, the journal *Annals of Internal Medicine* refused, citing the study’s strong methodology and data quality, and found no evidence of scientific misconduct.
Why Denmark’s Studies Undermine RFK Jr.’s Claims
Population-Scale Analysis: These studies are based on large, representative samples involving hundreds of thousands to over a million children over extended periods.
High-Quality Registry Data: With universal identifiers, Denmark achieved complete tracking and minimal participant loss, setting a gold standard in cohort design.
Consistent Null Findings: Multiple studies have consistently failed to link MMR, thimerosal, or aluminum with autism; no subgroup, period of onset, or clustering after vaccination has shown increased risk.
Methodological Transparency: While RFK Jr. has accused these studies of obfuscation or bias, journal editors and authors have countered these claims, providing clear explanations regarding privacy laws and study design.
Denmark has already addressed the question posed by RFK Jr.: vaccines do not cause autism. Decades of national registry data concerning MMR, thimerosal, and aluminum have shown no causal links. The argument for conducting new double-blind vaccinated vs. unvaccinated studies overlooks the substantial empirical evidence already available.
Policy discussions and public debates would benefit more from acknowledging this reality rather than advocating unscientific fears. Denmark’s large-scale, well-designed studies stand as a powerful counterpoint to vaccine-autism myths.
