What You Need to Know
In the first animal model of its kind, vaccinating pregnant mice with either of two capsular polysaccharide bioconjugate vaccines protected their pups from hypervirulent Klebsiella pneumoniae sepsis, with >80% survival in pups of immunized dams vs universal to high fatality in pups of unvaccinated dams.
Both 2- and 3-dose regimens produced detectable maternal IgG by day 21, and the antibodies reached pups via both the placenta and breast milk; the 3-dose regimen produced higher, longer-lasting titers through 6 weeks of age.
Although a single-dose vaccine would likely be preferred clinically, the investigators caution that murine findings may not translate directly to humans, whose prior exposure to Klebsiella antigens could allow even one dose during pregnancy to trigger a natural booster response.
The investigators report that both vaccines, in both 2- and 3-dose regimens resulted in detectable IgG maternal antibodies by day 21. Antibodies were transferred both prenatally via the placenta and postnatally through breastmilk. Although there were no detectable levels of polysaccharide-specific IgA found in breastmilk, there were significant levels of capsule-specific IgGs.They point out the likelihood of a different ratio in human breastmilk, which contains a higher percentage of IgA than IgG.
With parturition around day 21, the pups born to immunized dams demonstrated significant levels of polysaccharide-specific IgG through 6 weeks of age; with the 3-dose regimen associated with higher and longer-lasting titers then 2 doses. The investigators found the IgG antibodies functionally protective; with universal to high fatality in offspring of unvaccinated dams compared to >80% survival in pups born to immunized dams.
"Taken together, these data demonstrate that polysaccharide-specific IgG antibodies are detected in offspring of dams immunized with 2 or 3 doses of conjugate vaccine and that transferred antibodies may persist longer in pups born to dams vaccinated with the 3- dose regimen," Rosen and colleagues reported.
While a 2-dose regimen appeared effective in this animal model, the investigators expect that single dose immunization would be preferred in clinical application.Although this could be explored in animal models, they note that the findings do not necessarily translate, particular with animals that have been bred without encountering Klebsiella antigens prior to immunization.
"In humans, however, the possibility exists that the immune system may have already been exposed to specific Klebsiella antigens and thus even a single dose vaccination during pregnancy may induce a natural booster response," they posit.
Rosen and colleagues also anticipate that their murine model will help to elucidate other areas beside vaccine efficacy, including the contribution of maternal antibodies delivered through breastmilk vs placenta and how maternal vaccination affects bacterial colonization.
References
1. Wantuch PL, Tung J, Robinson LS, et al. Maternal vaccination with capsular polysaccharide bioconjugates protects against murine Klebsiella pneumoniae neonatal sepsis. Sci Adv. 2026; 12(42): eaeh8222. DOI: 10.1126/sciadv.aeh8222.
2. Wegorzewska M. Vaccinating moms protects offspring from deadly superbug. News Release, Washington University, St. Louis. 2026, October 12. https://medicine.washu.edu/news/vaccinating-moms-protects-offspring-from-deadly-superbug/.
