Seroprevalence of anti-pertussis antibodies and immunization status of pregnant women in Turin, 2019

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Abstract Background Pertussis is an acute respiratory infection caused by B. pertussis. An acellular vaccine is available, but the protection it confers is estimated to wane after 5 years. Infants under 6 months have the highest risk of complications and mortality. In Italy, the first dose of vaccine is administered in the third month of life and maternal vaccination is recommended in the final weeks of pregnancy. This study aimed to evaluate the seroprevalence of IgG antibodies to pertussis toxin (IgG anti-PT) among pregnant women as a potential source of transplacental transfer of antibodies, which may reduce neonatal risk of disease. Methods An observational cross-sectional study was conducted. Two hundred women between the 33rd and 37th weeks of pregnancy were recruited among patients undergoing routine pregnancy check-up at the S.Anna Hospital of Turin, from May to December 2019. Participants were interviewed on their immunization status and a serum sample was collected. Anti-PT levels were assessed using ELISA “NovaLisa B. Pertussis toxin (PT) IgG”. Lacking a correlate of protection, we have distinguished contact with microorganism (10-39 IU/mL), exposure in the previous 2-3 years (40-99 IU/mL), recent infection or immunization <12 months ( > =100 IU/mL). Results The median age of participants was 35. Women who had anti-PT titers > =10 IU/mL were 120 (60%) (10-39 IU/mL: 26%, 40-99 IU/mL: 14%, > = 100 IU/mL: 20%). Around 70.5% of women declared previous vaccination (42.5% during pregnancy). Among women vaccinated in the previous 12 months, 7% presented antibodies titer <100 IU/ml. Two women not vaccinated had a titer > 100 IU/ml, indicative of recent pertussis exposure. Conclusions This study found 40% of women with antibody titers under cut-off (<10 IU/mL) and 1% prevalence of recent exposure. Despite the late introduction of vaccination against pertussis during pregnancy, a good adherence to the program offered is evident. Key messages 40% of pregnant women in this study were lacking in antibodies against Pertussis and could not transfer anti-PT to their newborn for early protection. Improving maternal vaccination coverage against pertussis should be a public health priority in Italy; a good adherence to intervention was reported.