1. Two novel type 2 oral polio vaccines (OPV2s), OPV2-c1 and OPV2-c2, appeared safe and well tolerated when administered to healthy adults previously vaccinated with inactive poliovirus or monovalent OPV.
2. The novel OPV2s demonstrated an immunogenicity profile comparable to previously validated OPVs.
Evidence Rating Level: 1 (Excellent)
Study Rundown: Although poliovirus is generally considered to be eradicated, the wild-type 1 variant remains endemic in Afghanistan and Pakistan. Furthermore, although vaccines for poliovirus are now widely available, intestinal reversion to neurovirulence in areas with poor OPV coverage has been recorded in the Sabin oral poliovirus vaccine (OPV), which can be transmitted via stool and lead to paralysis. In response to this, two novel OPVs have been developed, OPV2-c1 and OPV2-c2, which primarily target wild-type 2 poliovirus, the main causative agent in polio neurovirulence reversion. This report includes results from two studies, a historical control phase 4 study of monovalent OPV2, which was removed from circulation during the development of novel OPV2 vaccines, and a phase 2 study evaluating the safety and efficacy of the two novel OPV2 vaccines versus placebo in those who previously received monovalent OPV or inactivated poliovirus vaccine (IPV).
Overall, in the phase 2 trial, most solicited adverse events reported for both novel OPV2s were mild to moderate (headache, fatigue, abdominal pain diarrhea) and rates were comparable to monovalent OPV2 recipients. However, rates of solicited adverse events were higher in the IPV groups compared to previous OPV. In the phase 4 trial of monovalent OPV2, seroprotection rate achieved was 97% (95% CI 92-99%), and 98% after two doses (95% CI 89-100). In the phase 2 trial of novel OPV2s, seroprotection rate was 100% after both the first and second dose of either OPV2-c1 or OPV2-c2. A major limitation of this study is the inability to directly compare monovalent OPV2 with the novel OPV2 vaccines, given that the former could only be tested in a historical control study. The monovalent Sabin OPV2 vaccine was withdrawn in 2016, making this impossible. Results of a similar study performed in pediatric populations were published simultaneously and can be found under the relevant reading.
Relevant Reading: Safety and immunogenicity of two novel type 2 oral poliovirus vaccine candidates compared with a monovalent type 2 oral poliovirus vaccine in children and infants: two clinical trials
In-Depth [randomized controlled trial]: This report of a partially masked, randomized history control phase 4 trial of monovalent OPV2 and a partially masked, randomized, control phase 2 trial of novel OPV2s enrolled 100 and 250 participants, respectively. Eligible individuals had previously received monovalent OPV in the phase 4 study, or either monovalent OPV or IPV in the phase 2 study, with no dose in the past year. The coprimary objectives of this study were to compare the safety and immunogenicity of the novel OPV2s versus monovalent OPV2 in individuals previously vaccinated with either monovalent OPV or IPV, respectively. Protocols for the phase 4 and phase 2 trials were created to be as similar as possible to allow comparisons. Participants in the phase 4 trial received either one or two doses of monovalent OPV2. Participants in the phase 2 trial received one or two doses of either OPV2-c1 or OPV2-c2 in those previously vaccinated with monovalent OPV, and two doses of OPV2-c1, OPV2-c2 or placebo in those previously vaccinated with IPV. Adverse events were separated as solicited (via a 7-day diary given to patient after first dose) or unsolicited.
Overall, no deaths or serious adverse events identified as related to vaccination were recorded. Rates of solicited adverse events for previously OPV-vaccinated patients were 62% of 100 for monovalent OPV recipients, 71% of 100 OPV2-c1 recipients, and 74% of 100 OPV2-c2 recipients. In participants previously IPV-vaccinated, solicited adverse events were higher, with 16 (94%) of 17 patients reporting at least one in the novel OPV2-c1 group, 13 of 16 (81%) in the OPV2-c2 group, and 15 of 17 (88%) in the placebo group. The seroprotection rate was 97% after one monovalent OPV2 dose and 98% after a second dose. In contrast, seroprotection rate was 100% at days 28 and 56 after receiving one dose either novel OPV2-c1 or OPV2-c2 candidates in patients previously vaccinated with OPV or IPV.
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