TUESDAY, Aug. 9, 2005 (HealthDayNews) -- A new large study by Danish researchers finds no basis for the common belief that multiple childhood vaccinations can increase the risk of infections from other diseases later in life.
According to the researchers, since the advent of multiple vaccines, it has been thought that vaccines such as measles-mumps-rubella or even aggregated vaccine exposure could lead to immune dysfunction, which can cause non-targeted infectious diseases resulting from a so-called overload mechanism.
In fact, the U.S. Institute of Medicine concluded in a 2002 report that there was strong evidence of biological mechanisms that could increase the risk of non-targeted infectious diseases from multiple vaccines.
But the Danish team points out there has not been any epidemiological and clinical support for this hypothesis, and some research has suggested that multiple vaccines have a beneficial effect on non-targeted infectious diseases.
"Vaccination is one of the most effective public health interventions and one of the safest," said lead researcher Anders Peter Hviid, an epidemiologist from the department of epidemiology research at the State Serum Institute in Copenhagen.
"In an era where childhood vaccination programs have succeeded in controlling a number of potentially very serious infectious diseases, the benefits of vaccinations are in danger of becoming obscured by vaccine safety scares," he added. "Continued evaluation is clearly important to test any issues of vaccine safety. This study should contribute to allaying any professional or parental concern over the safety of childhood vaccination."
Their report is published in the Aug. 10 issue of the Journal of the American Medical Association.
To prove their point, Hviid's team collected data on the 805,206 children born in Denmark from 1990 through 2001. The researchers collected data on the number, type and doses of the vaccines each child received. They also looked at those children who were hospitalized with infectious diseases, specifically acute upper respiratory tract infection, viral and bacterial pneumonia, septicemia, viral central nervous system infection, bacterial meningitis and diarrhea.
"Childhood vaccination does not increase the risk of infectious diseases not targeted by the vaccines," Hviid said.
Hviid's group found that of 42 possible associations from six vaccines and seven infectious disease categories, there was only one adverse association. This was for Haemophilus influenzae type b vaccine and acute upper respiratory tract infection. However, this association could be accounted for by chance alone and was not associated with the time the vaccine was given or the dose of the vaccine, they reported.
"Conversely, the 15 observed protective associations suggest that vaccination may have non-targeted protective effects," the researchers said in their report. "When considering aggregated vaccine exposure, we found no adverse associations between an increasing number of vaccinations and non-targeted infectious disease hospitalizations."
One expert sees these findings as supporting what is already well known.
"This study confirms what one would have imagined, based on what biologically makes sense and from everything else published to date," said Dr. Paul A. Offit, director of the Vaccine Education Center at the Children's Hospital of Philadelphia. "The number of vaccines that children receive in the first couple of years of life is well within the capacity of their immune system."
Offit pointed out that during the first week of life, a baby is exposed to hundreds of millions of bacteria. "What one sees in vaccines is a drop in the ocean of what one typically encounters and manages every day," he said. "You have about 10 trillion cells in your body. You have about 100 trillion bacteria in your body, to which you make an immune response. If you didn't make an immune response, they would overwhelm you."
Each bacterium has about 3,000 proteins, while vaccines have only a few, Offit said. "The diphtheria vaccine has one protein, the tetanus vaccine has one protein, the chickenpox vaccine contains 69 proteins," he noted. "If you add up all the vaccines that one could receive in the first years of life, it's about 130 immunologic components."
Another expert takes a contrary view of the study and vaccines in general.
"The concern about vaccines is not really with infectious diseases," said Barbara Loe Fisher, co-founder and president of the National Vaccine Information Center. "Our concern is with regression after vaccination and the huge increases in chronic immune and brain dysfunction in children."
Fisher said that the incidence of asthma, learning disabilities, ADHD, autism and diabetes has dramatically increased as the number of vaccines has doubled. "You can recover from infectious diseases, but you cannot recover from these permanent brain problems these children are having," she added, noting however that she did not know whether there was a direct connection between vaccines and the health problems she cited.
In addition, Fisher is concerned that the study did not include unvaccinated children. "Our experience has been that children who are not vaccinated are the healthiest children we have," she said.
Fisher said there is a need for studies that evaluate whether vaccination actually improves the long-term health of children. "We are potentially using too many vaccines," she said.
Moreover, Fisher believes that "there has been too much conflict of interest" in vaccination studies. The U.S. government, through the Centers for Disease Control and Prevention and the National Institutes of Health, along with the drug industry, control the money for vaccine research, Fisher said. "Because of this, researchers are very reluctant to come out with findings that are contrary to the prevailing policy of the government," she added.
The American Academy of Pediatrics can tell you more about vaccinations.