Vaccines are generally quite safe, but a recent study of BCG, DTP, and MCV raises concerns that warrant further exploration.
Although vaccines are generally considered quite safe, occasionally a child will experience a negative effect as a result of receiving one. At the request of WHO, a team of researchers from England, Greece, and the United States looked at a variety of clinical trials, cohort studies, and case-control studies to determine a possible relationship between particular vaccines and the subsequent death of a child.
The study was undertaken because of the understanding in the medical community that while vaccines have reduced the burden of diseases such as tuberculosis, measles, diphtheria, tetanus, and pertussis-especially in third-world countries where risk is high—under certain circumstances these vaccines may possibly increase the risk of illness and death from causes other than the diseases against which they protect. Furthermore, due to such possibilities, a large majority of the public continues to express anti-vaccine opinions.
The researchers reviewed data involving administration of the tuberculosis vaccine Bacillus Calmette-Guerin (BCG), which is commonly given in many countries other than the United States; diphtheria-tetanus-pertussis (DTP) vaccine (almost always given in conjunction with oral polio vaccine), which protects against all three conditions; and standard measles vaccine (MCV). The data came from locations as far-flung as Canada, Africa, South or Southeast Asia, and Haiti, and were collected anywhere from the 1930s to the late 2000s. Almost all of the studies providing the data were observational, with an acknowledged risk of many types of bias. However, the studies considered to be at very high risk of bias generally were excluded from the results.
After analyzing the information, the researchers concluded that, overall, the administration of the BCG vaccine to children generally reduced their expected mortality rate from any cause. The MCV vaccine also had a beneficial effect on expected mortality rates. The DTP vaccine, however, was associated with a higher than expected rate of mortality in most of the studies. This effect seemed to be stronger in female children than male ones, and it also seemed to be stronger when the DTP vaccine had been administered either along with or after the MCV instead of before the MCV. According to the researchers, it’s also possible that the effects could depend on whether a child had been receiving Vitamin A supplements, although there wasn’t enough information on the childrens’ supplementation status to draw any definite conclusions in that area.
Besides a certain lack of potentially important information such as Vitamin A supplementation status and the potential for bias in the form of confounding variables, the researchers note that another complication in their analysis was that the DTP vaccine was almost always administered in conjunction with oral polio vaccine, making it impossible to separate the effects of the two.
Based on their results, the researchers concluded that there was not enough evidence to justify an adjustment of the routine immunization schedule that WHO currently recommends for young children. However, they were clear that the findings warrant future studies on how vaccines—especially DTP—work on the immune system and what effects they have on illness and mortality, as well as how they may affect males and females differently. Until that information becomes available, the researchers stress that it’s important to keep babies on the recommended vaccine schedule.
Laurie Saloman, MS, is a health writer with more than 20 years of experience working for both consumer and physician-focused publications. She is a graduate of Brandeis University and the Medill School of Journalism at Northwestern University. She lives in New Jersey with her family.