A General Lack of IgG Against Pertussis Toxin in Chinese Pregnant Women and Newborns

Background: To investigate the level of pertussis-related antibodies in pregnant women and newborns. Methods: A total of 286 serum samples from healthy pregnant women and 221 cord samples from newborns were collected in 2016 in Beijing. A routine blood sample from pregnant women was obtained at 35 weeks of gestational age, and cord samples were collected in 20 minutes after delivery. The values from cord samples were used as the infant values. Anti-pertussis toxin (PT) IgG concentration was measured by ELISA (Euroimmun, Lübeck, Germany) using purified PT as a coating antigen. Newborns with anti-PT IgG ≤40 IU/mL in cord samples were considered to be unprotected against pertussis. Anti-PT IgG ≥100 IU/mL was considered to be indicative of a recent pertussis infection in pregnant women. Results: The anti-PT IgG concentration below the lower limit of detection (<5 IU/mL) occurred in 74.1% (212/286) of pregnant women and 66.5% (147/221) of newborns. Even with detectable anti-PT antibodies, the majority of pregnant women (79.7%, 59/74) and newborns (73.0%, 54/74) had antibody level of 5 to <20 IU/mL, and 13.5% (10/74) of pregnant and 14.9% (11/74) of newborns had antibody level of 20 to <40 IU/mL. The 75% percentiles for anti-PT IgG of pregnant women and newborns were 5.08 and 6.98 IU/mL, respectively. The prevalence of unprotected newborns as defined by anti-PT IgG ≤40 IU/mL was 95.9% (202/211). The prevalence of recent pertussis infection in pregnant women as defined by anti-PT IgG ≥100 was 0.7% (2/286). Conclusions: The pregnant women and newborns were generally lack of protective antibody and are vulnerable to pertussis in Beijing, China. Although acellular pertussis vaccine is administrated in infancy in China, a booster vaccination to pregnant women should be considered for protecting young infants who are too young to start pertussis vaccination.