Neither childhood immunizations nor H1N1 influenza vaccination increased the risk of inflammatory bowel disease, according to a meta-analysis of 11 studies in the August issue of Clinical Gastroenterology and Hepatology published online (2015 [doi:10.1016/j.cgh.2015.04.179]).
“Overall, our results did not find any significant increased risk of developing IBD after childhood immunization with BCG [bacille Calmette-Guérin], diphtheria, tetanus, poliomyelitis, smallpox, pertussis, measles, mumps, and rubella-containing vaccines,” said Dr. Guillaume Pineton de Chambrun of Lille (France) University Hospital and his associates. “The results of this meta-analysis are globally reassuring regarding the risk of developing IBD after childhood vaccination. Vaccines that are developed to protect against an infectious disease or its consequences are, for the majority, not a risk for the subsequent development of intestinal inflammatory disease.”
Besides the childhood vaccines, H1N1 vaccination was not linked to IBD in a single large study of adults (risk ratio, 1.13; 95% confidence interval, 0.97-1.32), the investigators said.
Controversies about immunizations and IBD date to at least 1995, when a report by Thompson et al. linked live measles vaccine to the disease (Lancet 1995;345:1071-4), said the investigators. “However, many publications after this report investigating vaccination with measles-containing vaccines did not show any association between immunization and IBD,” they emphasized. “Epidemiologic studies also investigated other vaccines such as BCG, diphtheria, tetanus, poliomyelitis, smallpox, pertussis, rubella, and mumps, reporting conflicting results.”
To further clarify the issue, they compared rates of IBD, Crohn’s disease, and ulcerative colitis among vaccinated and unvaccinated patients from eight case-control and three cohort studies published between 1970 and June 2014. When looking at IBD overall, 95% CIs for RRs all crossed 1.0, indicating no significant associations, they said. A subgroup analysis did link poliomyelitis vaccination with increased risk of developing Crohn’s disease (RR, 2.28; 95% CI, 1.12-4.63) or ulcerative colitis (RR, 3.48; 95% CI, 1.2-9.71), but the studies were dissimilar enough that the results need to be interpreted cautiously, they added.
To find the studies, the researchers searched MEDLINE, EMBASE, and the Cochrane central trials registry for randomized controlled trials, controlled clinical trials, cohort studies, and case-control studies published in any language and that included the terms ulcerative colitis, Crohn’s disease, inflammatory bowel disease, colitis, or ileitis. This approach yielded six population-based and two hospital-based case-control studies, and three population-based cohort studies. The studies of childhood immunizations included 2,399 patients with IBD and 33,747 controls, and the H1N1 study included 14,842 patients with IBD and almost 2 million controls, said the investigators.
The studies were “extremely heterogeneous” in terms of design, sample size, geographic location, and methods used to help patients recall their vaccination history, the investigators noted. “Vaccination protocols varied between countries and evolved through the years, with different types of vaccines and schedules leading to difficulties in risk evaluation,” they said. “Moreover, some vaccines used were live attenuated vaccines such as measles, oral poliomyelitis, or whole-cell pertussis vaccines, and may have a different effect on immune system activation and dysregulation, compared with other inactivated acellular vaccines.”
The Digitscience Foundation supported the research. The researchers declared having no conflicts of interest.