Do all those vaccines we give our children make them vulnerable to diseases not covered by the vaccines? No, a new study suggests.
Every parent soon learns that a visit to the pediatrician usually means it's time for another vaccination — often more than once. And some of these shots are a combination of vaccines.
There's a theoretical worry that all these immunizations overload a kid's immune system. According to this theory, the immune system is so busy handling vaccines it can't fight infections not covered by the vaccines.
Does this really happen? No, find Anders Hviid, MSc, and colleagues at the Statens Serum Institute, Copenhagen, Denmark. They report their findings in the Aug. 10 issue of The Journal of the American Medical Association.
"Our study should contribute to allaying vaccine-safety concerns," Hviid tells WebMD. "Our results are very convincing and very detailed and very thorough. With respect to infectious disease, yes, we think this shows that combination vaccines and vaccines in the aggregate are safe."
The study should put the issue to rest, says Walter A. Orenstein, MD, professor of medicine and associate director of the Emory Vaccine Center in Atlanta. Orenstein is the former director of the CDC's National Immunization Program.
"This study adds to the already substantial evidence that vaccinations do not increase the risk of other kinds of infections," Orenstein tells WebMD.
Looking for Disease Links
Hviid and colleagues had a lot to work with. They analyzed information collected on 805,206 children born in Denmark from 1990 though 2001.
The researchers reasoned that if vaccines made kids seriously ill, the kids would end up in the hospital. So they looked at all kids hospitalized for seven categories of infectious diseases. They then looked at whether any of these diseases could be linked to any of the six different vaccinations (including combination vaccinations such as measles-mumps-rubella).
Out of these 42 possible associations, only one came up weakly positive. The Haemophilus influenza type b vaccine — the Hib vaccine — was linked to acute respiratory tract infections in infants. This link is so weak that the researchers call it a chance finding.
"The exact finding was there was a 5 percent increased risk for upper-respiratory-infection hospitalizations with Hib vaccine," Hviid says. "At 5 percent this risk has no clinical significance, even if it is a real finding. And we believe it is a chance finding."
Why blame the single positive vaccine/disease link on chance?
—If the vaccine caused the respiratory infections, you'd expect to see most of these infections soon after vaccination. But the cases didn't cluster this way.
—If the vaccine caused the infections, kids who got the most vaccine would be most likely to get sick. But the kids who got the most Hib vaccinations were no more likely to get respiratory infections than those who got just one dose.
Combination Vaccines, Multiple Vaccinations Safe
"I view the data as very reassuring," Orenstein says. "The Denmark study adds a lot more strength to other studies showing that multiple vaccinations are safe. And it looks at a number of different vaccines and a number of different schedules and has multiple comparisons that weren't in the other studies. It reinforces the prior Institute of Medicine conclusions that these theoretical issues don't seen to be borne out in human experience."
One might argue that Danish kids don't get exactly the same vaccines as U.S. kids.
"It is not the U.S. childhood immunization schedule per se, but the vaccinations are a lot of times the same ones we use," Orenstein says. "The conceptual framework is the same."
Getting vaccinated against 12 diseases may sound like a lot. But that's nothing compared to what the body faces in the real world, says Frank DeStefano, MD, MPH, acting director of the CDC's immunization safety office.
"The body is always in contact with all kinds of bacteria and viruses — thousands and thousands of them — and our bodies, even the bodies of infants, handle that well," DeStefano tells WebMD. "Vaccinations are minuscule compared to what the body is bombarded with on a daily basis."
SOURCES: Hviid, A. The Journal of the American Medical Association, Aug. 10, 2005; vol 294: pp 699-705. Anders Hviid, MSc, Statens Serum Institute, Copenhagen, Denmark. Walter A. Orenstein, MD, professor of medicine, Emory University; associate director, Emory Vaccine Center, Atlanta. Frank DeStefano, MD, MPH, acting director, immunization safety office, CDC.