Childhood Vaccinations and Type 1 Diabetes

The incidence of type 1 diabetes (T1DM) has been increasing worldwide, with evidence suggesting that the increase may have begun in the middle of the last century. Because that’s about the time that mass childhood vaccinations began in developed countries, some have suggested that vaccinations may play a role.  The hypothesis goes that limited exposure to infectious diseases early in life, combined with increased use of childhood vaccinations, could increase the risk of T1DM.  In such a situation, developing T cells may acquire only a limited repertoire, and subsequently respond inappropriately to later infection.

But a new systematic review and meta-analysis – the first systematic review and meta-analysis to look at the link between routine childhood vaccinations and T1DM – has refuted this idea. The study was published online in Diabetologia.

“This study found no evidence that any of the reported vaccinations were associated with the risk of childhood type 1 diabetes,” wrote first author Eileen Morgan, MD, of Queen’s University Hospital Belfast (Ireland), and colleagues. “These findings were little altered after adjustment for potentially confounding factors. Results were also largely unchanged after two sensitivity analyses investigating the effect of study design and quality assessment score were conducted.”

The researchers used MEDLINE and EMBASE for studies published in any language from 1947 to July 2013 that evaluated the role of vaccination rates in children and the development of type 1 diabetes.  The analysis included 23 studies covering 13,323 cases of type 1 diabetes. Studies were mostly case-control in design, although the analysis included one randomized controlled trial. The majority were from Europe.

Results of fully adjusted analyses:

• Measles, mumps and rubella (MMR): pooled OR 0.53 (95% CI 0.21-1.38, P=0.19)

• Morbilli/measles: pooled OR 0.75 (0.54-1.05; P=0.09)

• Rubella/German measles: 0.85 (0.58-1.26; P=0.43)

• Parotitis/mumps: 0.81 (0.59-1.11; P=0.20)

• Pertussis/whooping cough: 0.79 (0.53-1.18; P=0.25)

• BCG: 0.96 (0.76-1.21; P=0.73)

• Haemophilus influenza B (HiB) vaccines: pooled OR 1.07 (0.97-1.17; P=0.17)

• Tetanus: 0.76 (0.43-1.34; P=0.34)

• Diphtheria: 0.99 (0.49-2.00; P=0.98)

• Polyomyelitis: 0.80 (0.39-1.68; P= 0.56)

• DTP: 0.90 (0.15-5.31; P= 0.91)

• Significant heterogeneity between studies

Few studies analyzed the association between timing of vaccinations and the development of T1DM, the authors noted, so the meta-analysis could not look at this issue. Because mouse studies have suggested that timing of vaccination may influence the development of T1DM, future research should look at this issue, they added.

“[T]his systematic review and meta-analysis does not show evidence of an association between any of the routine vaccinations investigated and childhood type 1 diabetes,” they concluded, “Therefore, this study does not provide a rationale for altering vaccination programmes based upon a subsequent risk of type 1 diabetes.”

Take-home Points

• Rates of T1DM have been increasing since about the time that childhood vaccinations became widespread in developed countries, leading some to speculate that vaccinations could play a role in rising rates of T1DM.

• A recent meta-analysis and systematic review found no evidence to support a link between routine childhood vaccinations and T1DM.

Reference: Morgan E, et al. Vaccinations and childhood type 1 diabetes mellitus: a meta-analysis of observational studies. Diabetologia. Epub ahead of print 12 Nov 2015.