Infants who receive antibiotics may have a weakened response to vaccinations. Scientists have long been aware that some children have lower antibody responses to vaccinations than others, but the reason for the differing response is unknown. This recent study may shed light on what’s going on.

The study looked at antibody responses to 4 common vaccinations in 560 infants and toddlers. 61% of the children had received antibiotics at least once. Compared to those who hadn’t received antibiotics, the vaccine antibody response was “sub-protective” in the antibiotic group. In fact, the more antibiotics the children received in the first year of life, the lower their vaccine antibody levels were between 12 and 15 months.

Why do antibiotics have such a profound impact on vaccine antibody response? Because antibiotics wipe out beneficial gut bacteria – the very bacteria that help to develop and guide the immune system. Without a balanced microbiome, the immune system isn’t able to function properly. Researchers who conducted the study stress the importance of judicious use of antibiotics. For more information for parents and antibiotic use in children, check out Antibiotic Prescriptions for Children: 10 Common Questions.