ABOVE: © iStock.com, Daniel Balakov

A study published yesterday (April 27) in Pediatrics finds that children who received a course of antibiotics during the first two years of life had diminished immune responses to four common vaccines. Researchers tell Science News that the findings are a cautionary tale about overusing antibiotics.

Babies are typically immunized against various diseases in the first six months of life and get boosters in their second year. From 2000 to 2016, the study’s authors collected blood samples from 560 children ages 6 to 24 months during routine visits with their pediatricians, measuring antibody levels after the children received polio, diphtheria-tetanus-pertussis, Haemophilus influenzae type b, and pneumococcal vaccines. 

Of these children, 342 had collectively been prescribed close to 1,700 courses of antibiotics. The other 218 children had not received antibiotics. The team analyzed whether antibody levels induced by the four vaccines met the threshold of what is considered protective and found that at 9 and 12 months old, children who had received a course of antibiotics were significantly more likely to have subpar levels of antibodies than those who had not. The immune response was lower among children who’d had multiple courses of antibiotics than for those who’d had one, with each antibiotics dose associated with 5 to 11 percent lower antibody levels after initial vaccinations and 12 to 21 percent lower antibodies after booster shots. 

The study did not assess the children’s actual rates of disease, and some studies have noted that antibody levels are sometimes imperfect predictors of immune protection against disease. 

“If anyone needed yet another reason why overprescription of antibiotics is not a good thing, this paper offers that reason,” immunologist Bali Pulendran of Stanford University School of Medicine, who was not involved in the study, tells Science News. 

The association varied with the type and length of antibiotic treatment. Broad spectrum drugs, which target a wide array of bacteria, were associated with antibody levels below what is protective, while more targeted antibiotics were not. Ten-day courses, but not five-day courses, were associated with reduced vaccine-induced antibody levels. 

Antibiotics are known to affect the gut microbiome, which in turn influences a wide array of bodily systems, including the immune system. The study’s authors suggest that antibiotics might negatively affecting children’s gut health by decreasing the diversity of bacteria in the gut, which may in turn decrease vaccine effectiveness. Science News reports that this new study adds to existing evidence that gut health may affect response to vaccination.

See “Gut Microbes Boost Flu Vaccine’s Success: Clinical Trial

According to Science News, study coauthor Michael Pichichero, a pediatric infectious diseases specialist at the Rochester General Hospital Research Institute in New York, and colleagues are beginning a study with a new group of children to see what kinds of changes are occurring in the gut bacteria. The researchers plan to collect stool samples along with blood draws and antibiotic use records. They’d like to follow the children past age 5, beyond the time kids receive another round of booster shots, to learn whether antibiotics also interfere with this next opportunity to develop antibodies.

“Antibiotics are miracle medicines,” Pichichero tells Science News. “In no way does this study imply that children who need an antibiotic shouldn’t get it.”