Australian researchers have found that newborns treated with antibiotics within their first few weeks of life exhibited a weakened immune response to vaccines. The root cause was traced to lower levels of Bifidobacterium, a beneficial gut bacterium commonly found in healthy infants, said the study published in the Nature journal.
As per the study, the research team followed 191 healthy, vaginally delivered infants from birth to 15 months of age. Nearly 86% of the infants received a hepatitis B vaccine at birth, followed by routine childhood vaccine starting at six weeks, in line with the Australian National Immunization Program.
To understand the impact of antibiotics, researchers grouped the infants based on their exposure such as those who had no direct or maternal antibiotic exposure, with maternal antibiotic exposure only and the third category included those having direct neonatal antibiotic exposure for at least 48 hours.
To assess immune response and gut microbiota composition, the team collected stool samples at 7 days and 6 weeks, and blood samples at various intervals between 6 weeks and 15 months. To prevent bias, the sample collectors remained unaware of the infants’ exposure categories.
The findings revealed that infants who were directly exposed to antibiotics after birth produced significantly lower levels of antibodies in response to several polysaccharides included in the 13-valent pneumococcal conjugate vaccine (PCV13). In contrast, maternal antibiotic exposure alone did not have the same effect.
The PCV13 vaccine is designed to protect against Streptococcus pneumoniae, a dangerous bacterium that causes pneumonia, blood infections, and meningitis. The bacteria are shielded by a capsule made of polysaccharides, which helps them evade the immune system. The vaccine improves immune detection by linking these polysaccharides to proteins, prompting antibody production.
However, antibiotic use in the neonatal period disrupts this immune response, making the vaccine less effective.
To explore the biological mechanism, scientists conducted additional experiments on germ-free mice. These tests confirmed that a reduced abundance of Bifidobacterium in the gut microbiome was responsible for the lower immune response. Remarkably, supplementing the mice with a mix of Bifidobacterium species or Infloran—a probiotic widely used in infants—restored the immune response to PCV13.
Based on their findings, researchers suggest that restoring Bifidobacterium-rich gut microbiota in infants who receive early antibiotics could significantly improve vaccine responses. Administering probiotics such as Infloran before vaccinations may lead to stronger immunity and better protection against life-threatening infections
Dr. Sangeeta Sharma, Professor at Delhi-based Institute of Human Behaviour & Allied Sciences (IHBAS) echoed similar concerns asserting that, “antibiotics save lives, no doubt. But their indiscriminate or early use, especially in the neonatal period, may carry hidden costs. This study adds to the growing body of evidence emphasizing the microbiome’s essential role in immune system maturation and vaccine efficacy.
“In low- and middle-income countries, where infections in newborns are frequent and empirical antibiotic use is common, these findings have important policy and practice implications. They call for greater antibiotic stewardship even in neonatology, careful weighing of risks and benefits.”
As we confront the dual challenge of rising antimicrobial resistance and suboptimal vaccine responses, this study reminds us: in protecting the youngest, we must look beyond immediate cures to long-term consequences, added Dr Sharma who also heads Delhi Society for Promotion of Rational Use of Drugs (DSPRUD), an organisation engaged in spreading awareness about the misuse and importance of antibiotics.