The change in pertussis antibody titers before and after pertussis vaccination in infants in Jinan

Objective The objective of this study is to asses the protective efficacy of the current immunization schedule in infants aged 1-8 months in Jinan by comparing pertussis toxin IgG antibody (PT-IgG) levels pre- and post-vaccination. The research will delve into the variation in antibody levels among different age groups and after various doses of the vaccine aiming to provide scientific evidence for optimizing pertussis immunization strategies.Methods Serum samples and clinical information were collected from infants aged 1 to 8 months who visited Jinan Children's Hospital from June 2023 to July 2024. PT-IgG levels were measured using enzyme-linked immunosorbent assay (ELISA). Statistical analyses were performed using SPSS version 29.0.Results A total of 303 infants aged 1-8 months were enrolled in this study,including 45 confirmed cases of pertussis, and 258 cases without no history of pertussis infection. In the infection group, the pertussis antibody levels were significantly higher in boys than in girls (Z=-2.505, P=0.012), while there were no notable gender- based variations (Z=-0.216, P=0.829)in the non-pertussis infection group. Among the pertussis infection group, 46.47% (21/45)of infants did not complete the vaccination on time, and the corresponding rate was 38.76% (100/258)in the non-pertussis infection group. Significant differences in PT-IgG levels were observed across vaccination doses (χ²=33.801, P=0.000). The proportions of unvaccinated infants (89.63%, 121/135)and those who received one dose of vaccine (91.67%, 33/36)were significantly higher in the PT-IgG<40 IU/mL group. Among infants with PT-IgG levels in the 40-100 IU/mL group, the proportion of those who received three doses of vaccine (34.92%, 22/63)was significantly higher than that of the unvaccinated group (9.63%, 13/135)and the one-dose group (8.33%, 3/36). The proportion of those who received two doses (25.00%, 6/24)was significantly higher than that of the unvaccinated group. In the PT-IgG>100 IU/mL group, the proportions of individuals who received two doses (12.50%, 3/24)and three doses (6.35%, 4/63)were significantly higher than that of the unvaccinated group (0.74%, 1/135)and the one-dose group (0.00, 0/36). Significant differences in PT-IgG distribution existed across age groups (χ²=13.863, P=0.004). In the group with PT-IgG＜40 IU/mL, the proportions of infants aged 1 to less than 3 months (89.47%, 51/57)and infants aged 3 to less than 6 months (85.29%, 87/102)were significantly higher than that of infants aged 6 to less than 9 months (68.69%, 68/99). Among infants aged 6 to less than 9 months, the proportion of those with PT-IgG levels between 40 and 100 IU/mL (27.27%, 27/99)was higher than those of the other two groups.Conclusion As the DTaP vaccine doses increases, pertussis antibody titers gradually rise in infants aged 1-8 months in Jinan, with protective efficacy gradually enhancing. Significant protective effects can be achieved after the 2-dose primary vaccination series. However, the phenomenon of delayed vaccination leads to a postponement of the production of protective antibodies in infants, resulting in a higher risk of pertussis infection for infants of a younger age.