Exposure to antibiotics as a newborn can impair immune response to vaccines

 Immunization programs save millions of lives every year by protecting against preventable diseases. The immune response to vaccines, however, varies significantly between individuals, and the results can be suboptimal in populations at a higher risk of developing infectious diseases. Growing evidence suggests that differences in gut microbiota could be a key factor driving these variations.

A recent Australian study published in Nature found that babies treated with antibiotics within the first few weeks of their life showed weaker immune response to vaccines due to reduced levels of Bifidobacterium—a bacterial species that lives in the human gastrointestinal tract. Replenishing Bifidobacterium in the gut microbiome using probiotic supplements such as Infloran showed promising results in restoring the immune response.

The researchers followed 191 healthy, vaginally born infants from their birth to 15 months: 86% of the participants received the hepatitis B vaccine at birth, and, by six weeks of age, began their routine childhood vaccinations, according to the Australian National Immunization Program schedule.

The infants were grouped based on their exposure to antibiotics: no direct or maternal exposure, exposed to maternal antibiotics and received at least 48 hours of antibiotic treatment during neonatal care.

To monitor changes in gut microbiome and vaccine-related immune responses over time, stool samples were collected at seven days and six weeks of age, while blood samples were taken at multiple points between six weeks and 15 months. To prevent bias during sample collection and analysis, the researchers collecting the samples weren't aware of which infants belonged to which exposure group.

Vaccine-specific antibody responses are frequently impaired in infants directly exposed to antibiotics in the neonatal period. Credit: Nature (2025). DOI: 10.1038/s41586-025-08796-4

The investigation revealed that children who were directly exposed to neonatal antibiotics, not the ones exposed to maternal antibiotics, produced much lower levels of antibodies against multiple polysaccharides included in the 13-valent pneumococcal conjugate vaccine or PCV13 vaccine.

Streptococcus pneumoniae, a bacteria known for causing serious diseases like pneumonia, blood infections, and meningitis, is surrounded by a capsule made up of polysaccharides, or sugar molecules that help the bacteria evade attacks by the body's immune system.

The PCV13 vaccine makes it easier for the immune system to attack S. pneumoniae and produce antibodies by linking the polysaccharide capsule layer to proteins. Exposure to neonatal antibiotics reduces antibody production against such polysaccharides, weakening the immune response.

Experiments on germ-free mice revealed that the lower immune response was linked to a reduced abundance of Bifidobacterium in the gut microbiome. However, giving the mice a mix of Bifidobacterium species or Infloran, a commonly used infant probiotic, helped reverse the negative effects of antibiotics and regain the immune response to PCV13.

The researchers propose that restoring a healthy Bifidobacterium-rich microbiota in antibiotic-exposed infants before their vaccination might enhance the antibody responses to vaccination, leading to better protection against infectious diseases.

More information: David Lynn, Bifidobacteria support optimal infant vaccine responses, Nature (2025). DOI: 10.1038/s41586-025-08796-4. www.nature.com/articles/s41586-025-08796-4

https://medicalxpress.com/news/2025-04-exposure-antibiotics-newborn-impair-immune.html