Outer membrane vesicle based pertussis vaccine (Intravacc)

Objective: To evaluate the protective effectiveness (VE) of the acellular pertussis vaccine (aPV) against pertussis in children aged 2 months to 6 years. Methods: A test-negative case-control study was conducted among children aged 2 months to 6 years who sought medical care for cough and underwent pertussis nucleic acid testing at sentinel surveillance hospitals in Zhejiang Province in 2024. Cases were defined as those with positive pertussis nucleic acid test results, while controls were test-negative individuals matched 1∶1 based on propensity scores using the caliper matching method. Conditional logistic regression models were used to calculate odds ratios (ORs) and VEs. Results: Among the 658 participants, 31.76% (209 cases) tested positive for pertussis. After propensity score matching, 203 cases and 203 controls were included in the analysis. The VE of 1-2, 3, and 4 doses of aPV against pertussis was 52.46% (95%CI:-39.82%-83.84%), 65.22% (95%CI: 6.86%-87.02%), and 72.21% (95%CI: 34.33%-88.24%), respectively. For pertussis-related hospitalization, the VE of 1-3 and 4 doses was 80.95% (95%CI:31.38%-94.71%) and 86.79% (95%CI: 51.89%-96.37%). The VE for those who completed 4 doses of vaccination and had intervals of less than 2 years, 2 years, 3 years, and 4 years or more after vaccination were 91.15% (95%CI: 67.61%-97.58%), 84.70% (95%CI: 43.71%-95.84%),56.23% (95%CI:-47.58%-87.02%), and 49.92% (95%CI:-83.74%-86.35%), respectively. Conclusion: The VE of aPV against pertussis in children aged 2 months to 6 years increases with the number of doses administered, and it is more effective in preventing hospitalization due to pertussis. The VE declines rapidly over time after the last dose. It is recommended to follow the new pertussis immunization program for timely and full vaccination.

Bordetella pertussis produces pertussis toxin (PT) as a major virulence factor; detoxified PT is an essential antigen for acellular pertussis vaccines. The toxicity of PT (residual toxicity and reversion to toxicity) in pertussis vaccines has long been assessed using the mouse histamine sensitization test (HIST). In this study, as an alternative to animal safety testing-based HIST, a 96-well in vitro assay (fetuin-ADP-ribosylation assay), which assesses both the ADP-ribosyltransferase of the S1 subunit and the carbohydrate-binding activities of the B-oligomer in PT, was developed and evaluated for its applicability to the final products of acellular pertussis combination vaccines, DPT, DPT-IPV, and DPT-IPV-Hib. The fetuin-ADPR assay is based on a two-step process: (i) recovery of PT antigen with retained carbohydrate-binding activity from vaccine samples using fetuin-coated magnetic beads, and (ii) measurement of ADP-ribosyltransferase activity of the recovered PT antigen using a 96-well microplate immobilized with the target molecule, Gα_i3C20 peptide. In the assay system, the standard curve of the PT reference NIBSC 90/518 exhibited a linear response up to 320 ng/mL (R² ≥ 0.98). The fetuin-ADPR assay showed that the activatable PT content in most final vaccine products stored at 4 °C was <20 ng/mL (below the detection limit), whereas that in vaccines stored at 37 °C for 28 days ranged from <20 to 159.7 ng/mL. The assay successfully detected the reversion to toxicity of detoxified PT. Validation of the fetuin-ADPR assay showed a day-to-day reproducibility of 27.5 % coefficient of variation and 44-50 % accuracy as assessed by spike recovery. The fetuin-ADPR assay has the advantage of being performed in a 96-well plate with standard laboratory equipment, and is a promising alternative to in vivo HIST for assessing PT toxicity in the final products of acellular pertussis combination vaccines.