Vaccine- and infection-induced pneumococcal and DENV-NS1 antibodies reveal differential transplacental transfer and maternal-infant early exposure burden.

BACKGROUND

Pregnant women and their infants are vulnerable to severe infections with S. pneumoniae and dengue virus (DENV), for which early protection depends on maternally derived antibodies. Infection- and vaccine-induced responses may differ in quality and transfer, with implications for maternal immunization strategies. We evaluated isotype-specific antibody responses to pneumococcal vaccination and natural DENV infection in pregnant women and their infants and quantified early postnatal DENV exposure.

METHODS

In a longitudinal cohort in southern Colombia, a DENV-hyperendemic region, 140 low-risk pregnant women received either PPSV23 or Hib conjugate vaccine randomly in the third trimester. Circulating pneumococcal serotype 23F (Pn23F)-specific IgG and DENV NS1-specific IgG, IgM, and IgA were measured by ELISA in maternal, cord, and infant at delivery, 3, and 6 months; circulating NS1 was used to detect active DENV infection. Postnatal clinical follow-up was performed until 6 months of age.

RESULTS

PPSV23 increased maternal anti-Pn23F IgG, whereas anti-NS1 IgG from natural infection remained stable. Anti-Pn23F and anti-NS1 IgG were detectable in cord blood, but maternal-cord levels were strongly correlated for anti-NS1 IgG and not for anti-Pn23F IgG. Infant anti-NS1 IgG seropositivity declined from 99% at birth to 74% at 6 months, while anti-Pn23F IgG levels in infants of PPSV23-vaccinated mothers remained stable. Despite 99.1% maternal anti-NS1 IgG seroprevalence, 13.1% of infants developed anti-NS1 IgM or anti-NS1 IgA by 6 months, indicating early DENV infection without NS1 antigenemia or clinically apparent dengue.

CONCLUSION

Vaccine- and infection-induced antibodies showed antigen- and isotype-specific differences in transplacental transfer and postnatal persistence, revealing a high burden in the maternal and early infant populations. The emergence of NS1-IgA in infants demonstrates active postnatal DENV transmission and supports NS1-IgA as a sensitive marker for early infant exposure and serosurveillance in hyperendemic settings.