Babies usually get their first shots in their first six months of life, but if they get an infection, antibiotics are also waiting for them. Rochester Central Hospital Research Institute and Rochester Institute of Technology have been comparing vaccine responses in children aged six months to one year for ten years: some of the babies received antibiotics, some did not. There were four types of vaccines: combined against diphtheria, tetanus and whooping cough, against poliomyelitis, against pneumococci and against Haemophilus influenzae. The research results are published in the journal Pediatrics.

Antibiotics reduce the effectiveness of vaccines: with them, the level of corresponding antibodies that developed immunity against vaccine pathogens decreased, and the more antibiotics a child was given, the less antibodies he had, writes Science and Life.

At the first vaccination, the level of antibodies fell by an average of 5-11% for each antibiotic course; when children were given a booster (an extra dose of vaccine) in their second year of life, the levels of the same antibodies dropped by 12–21% with each course of antibiotics.

At the same time, broad-spectrum antibiotics lowered the level of vaccine antibodies more than antibiotics with a specific target, and if the treatment was extended for ten days, then this affected vaccine immunity worse than when antibiotics were given only five days. Antibiotics kill not only harmful bacteria, but also beneficial symbionts in the intestinal microflora.

Obviously, due to losses in the microflora after a course of antibiotics, children's immunity cannot respond effectively enough to the vaccine. And this is not so new: the first suspicions that the microflora is important in vaccination appeared almost twenty years ago.