Despite human papillomavirus type 6 or 11 (HPV6/11) being often vertically transmitted from mothers with condyloma acuminata (CA) to their infants, HPV-related neonatal mucosal diseases are rare. The role of maternal anti-HPV6/11 neutralizing antibodies in preventing the vertical transmission remains to be unknown because of lack of the neutralization assay system of HPV infection. We experienced two cases of HPV6-positive CA during pregnancy. Neutralizing antibodies against HPV6 in maternal, umbilical, and infantile sera were determined using a surrogate assay system to monitor HPV6 pseudo-infections. The neutralizing antibodies were detected in maternal and umbilical sera and in serum of one of the infants tested at 5 weeks old. In the infant exposed to HPV6 at birth, viral DNA was not detectable in the oral cavity 5 weeks after birth. This is the first report to describe that neutralizing antibodies against HPV6 in mothers with CA go through the placenta and enter the circulation of their infants. These data may provide a mechanistic paradigm for the prevention of its vertical transmission.

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