Immunogenicity and Safety of Purified Vero Cell Rabies Vaccine (PVRV) Produced by Liaoning Cheng Da Co. Under Zagreb 2-1-1 or 5-dose Essen Regimen in Chinese Adults Aged 50 and Above

Background: Two kinds of regimens (2-1-1 and 1-1-1-1-1) can be selected after Zagreb regimen(2-1-1)of PVRV was officially approved in Beijing in January 2015. Up to now, the subjects for most studies about the comparison between Zagreb and Essen regimen are under 50 y old, rarely at and above. Aging of the immune system may result in decreasing efficacy of vaccination, especially for adults aged above 65-70 y. This study compared the safety and immunogenicity of the Zagreb and Essen regimen in Chinese adults aged 50 and above with the goal to provide a supplemental data for this age group.

Methods: A total of 114 cases were divided into 2 groups randomly, received PVRV under the Zagreb and Essen regimens respectively. Serum samples were collected at D0, D7, D14, D42, D180 and D365 to determine the rabies serum neutralizing antibody by rapid fluorescent focus inhibition test (RFFIT). Safety analyses were made by comparing the AEs in day-3, day-7, and day-(7 + 21) in Zagreb or day-(7 + 28) in Essen by gender and age cohorts.

Results: 617 blood samples were obtained. Two groups showed similar immunogenicity, the neutralizing antibody titer of all subjects at D14 and D42 showed >0.5 IU/ml. Under the same regimen, Subjects ≥65 y had lower GMC than those who <65 years from D7 to D365 within 2 groups. This difference was significantly shown on D7, D14, D180 in Zagreb group, and on D180 in Essen group (t = 2.38, p = 0.02; t = 3.78, p < 0.001; t = 2.30, p = 0.03; t = 4.42, p < 0.001). Subjects<65 years had higher seroconversion rate compared to ≥65 y on D7, D180 and D365 in both 2 groups, this difference was also significantly shown on D180, D365 in Zagreb group and on D180 in Essen group (χ = 20.66, p < 0.001; χ = 6.56, p = 0.02; χ = 10.96, p = 0.002). Two regimens all showed favorable performances with mildly or common adverse events (AEs). The incidence of local AEs after 3 d in Essen group was higher than Zagreb group (χ = 9.69, p = 0.002). The most common local AE was pain, the incidences (8.8%) in Zagreb group was higher than Essen group (8.4%, χ = 5.12, p = 0.02). All AEs for Zagreb group and 52.3% of AEs for Essen group occurred during the first 72 hours. During the first 72 hours, subjects aged <65 in Zagreb group (16.26%) had higher incidences of AEs than Essen group (8.57%, χ = 4.54, p = 0.03), males in Zagreb group (16.05%) had higher incidence of AEs than Essen group (5.71%, χ = 5.34, p = 0.02). The incidences of AEs close in during the first 7 d.

Conclusion: The Zagreb and Essen regimens demonstrated the similar safety and efficacy of PVRV in Chinese adults aged 50 and above. People ≥65 y showed reduced immune response to both regimens. More AEs for the Zagreb regimen were observed within the first 72 hours, especially for male and people < 65 y.