Messy mix? Combined vaccine yields fewer antibodies.

Thanks to modern medicine, children in the United States can look forward to receiving up to 20 vaccinations during early childhood. It's all for a good cause, but try telling that to a baby.

Scientists attempting to minimize the number of injections by bunching together vaccines now report the curious finding that one of the component vaccines doesn't seem to work as well in combination as it does when administered by itself. Moreover, two other vaccines administered with the combination vaccine also lost some of their protective potency.

Researchers in England randomly chose 119 infants to vaccinate against group C meningitis in a series of shots. Another 115 infants got a combination vaccine called 9-valent, which includes the group C meningitis vaccine and eight others for various types of meningitis and pneumonia.

At each of three monthly visits, both groups of infants also received a shot containing vaccines against diphtheria, whooping cough, tetanus, and the type of meningitis caused by Hemophilus influenzae bacteria (Hib). They received oral polio vaccine, too. Thus, each child got two shots and an oral polio dose at 2, 3, and 4 months of age.

Blood drawn from the infants at age 5 months showed that the children who had received the 9-valent vaccine had made only one-fourth as much antibody against group C meningitis as had the infants getting the meningitis-only vaccine, the researchers report in the April 13 Journal of the American Medical Association.

Also, infants getting the 9-valent shot made significantly less antibody for fighting diphtheria and Hib meningitis than did those getting the simple group C meningitis shots, says study coauthor Jim R Buttery of the Murdoch Children's Research Institute in Melbourne, Australia. Buttery worked on the study while at the University of Oxford in England.

"This study doesn't rule out that [polyvalent] formulations might work well," says Sally A. Quataert of the University of Rochester in New York. Rather, it shows that polyvalent-vaccine studies need to be rigidly controlled, she says. For example, the group C meningitis vaccine given to children as part of the 9-valent shot came from a different batch of vaccine than did that given on its own, leaving room for differences, she says.

Buttery suspects that the volume of certain ingredients in a 9-valent vaccine might be at fault for the multivaccine's poor performance when given in combination with other vaccines. He points specifically to the large amounts of carrier proteins--molecules added to vaccines to boost immunity--in the formulation of the 9-valent vaccine. Researchers now need to ascertain whether these proteins might actually be interfering with the immune response, says Buttery.

Wyeth, the Madison, N.J.-based company that developed the 9-valent vaccine, funded the study. Last year, the company dropped efforts to market the 9-valent vaccine in the United States so that it could concentrate on Prevnar, a 7-valent vaccine that is widely used for prevention of meningitis and pneumonia. Meanwhile, Wyeth is developing a 13-valent vaccine that would protect children against group C meningitis and 12 other strains of bacteria that cause meningitis, pneumonia, or the blood infection septicemia.