Level 2 [mid-level] evidence
Measles outbreaks continue throughout the world, resulting in more than 100,000 deaths each year and millions of dollars spent to treat and prevent the spread of the disease. In 2019, more than 1270 new cases of measles were reported in the United States, the largest report of new cases since 1992. According to the Centers for Disease Control and Prevention, more than 73% of the cases were linked to outbreaks in New York State and were concentrated in communities where children were unvaccinated.1
Parents who choose not to vaccinate their children with the highly effective measles, mumps, and rubella (MMR) vaccine provoke a variety of responses from clinicians, ranging from gentle frustration to outright anger. The vaccine prevents upward of 95% of clinical measles cases, yet rates of vaccination have declined precipitously since a fraudulent report published in The Lancet in 1998 associated the vaccine with the onset of autism; the report has since been retracted.2 There are numerous more recent reports demonstrating time and time again that there is no association between MMR vaccination and autism. Now we have another study that clinicians can use as they engage parents in an effective conversation about vaccination.
A Danish cohort study examined the association of MMR vaccination with the risk of developing autism spectrum disorder among more than 650,000 children born from 1999 to 2010 from data that linked both vaccination and disease data sets.3 Children with a diagnosis of autism before 1 year of age and those with conditions tightly linked to autism (such as DiGeorge syndrome) were excluded from the analysis.
The authors used data from the Danish national registration system to generate an autism risk score, which included advanced maternal and paternal age, method of delivery, 5-minute APGAR, preterm birth, head circumference, birth weight, and smoking in pregnancy.3 More than 95% of all children received the MMR vaccine. During the same period, 6517 children were diagnosed with autism spectrum disorder as defined by the Danish Psychiatric Central Registry, which contains diagnoses assigned by child psychiatrists.
Regression analysis was used to produce hazard ratios according to vaccine status and adjusted by birth year, sex, other vaccines received, sibling history of autism, and the risk score. The adjusted hazard ratio for the development of autism showed lower risk in the MMR-vaccinated group compared with the unvaccinated group, although the difference was not statistically significant (hazard ratio, 0.93; 95% CI, 0.85-1.02). In addition, receipt of the MMR vaccine did not increase the risk for autism among high-risk groups, including those with a sibling with autism or high autism risk score.
This study adds to robust data demonstrating that MMR vaccination is not associated with autism. This large real-world data set demonstrates that even among children at the highest risk for autism spectrum disorder, MMR vaccination does not increase their risk of developing autism. For parents who are hesitant about having their child vaccinated, bringing fresh data to the table and discussing the facts may help temper the emotions in the room. Although scientists and researchers may wonder why we need yet another publication to further debunk the myth linking MMR vaccination to autism, for some parents, seeing new data may help them move a bit closer to seeing the truth.
1. Centers for Disease Control and Prevention. Measles cases and outbreaks. CDC website. https://www.cdc.gov/measles/cases-outbreaks.html. Updated January 6, 2020. Accessed January 7, 2020.
2. Wakefield AJ, Murch SH, Anthony A. Ileal-lymphoid-nodular hyperplasia, non-specific colitis, and pervasive developmental disorder in children. Lancet. 1998;351(9103):637-641. Retracted.
3. Hviid A, Hansen JV, Frisch M, Melbye M. Measles, mumps, rubella vaccination and autism: a nationwide cohort study. Ann Intern Med. 2019;170(8):513-520.