The persistent transmission of wild poliovirus in Pakistan and Afghanistan underscores the need for effective, adaptive outbreak response strategies. As of 2021, these two countries remain the only regions where indigenous WPV1 circulation continues, while widespread cVDPV2 outbreaks have further complicated eradication efforts. The strategic choice of vaccine for outbreak response—particularly between trivalent OPV (tOPV), monovalent OPV serotype 2 (mOPV2), and bivalent OPV (bOPV)—has significant implications for both immediate outbreak control and long-term public health outcomes.
A dynamic transmission model was developed to simulate the impact of different vaccine options on poliovirus spread across Pakistan and Afghanistan. The model incorporates detailed population structure, including a high-risk under-vaccinated subpopulation representing 5% of Pakistan’s and 10% of Afghanistan’s total populations. It accounts for seasonal variation in transmission, heterogeneous mixing patterns, waning immunity, and the evolution of OPV strains from attenuated Sabin to fully reverted cVDPV forms. Crucially, the model integrates disruptions caused by the COVID-19 pandemic, including reduced routine immunization coverage and restricted movement due to lockdowns and border closures.
Simulations compare four vaccination scenarios: a base case using bOPV and mOPV2 as per prior plans; “tOPV use 2021 only,” which uses tOPV exclusively in 2021; “tOPV use,” which replaces selected bOPV rounds with tOPV through 2023; “tOPV and mOPV2 use,” combining tOPV with targeted mOPV2 responses; and “mOPV2 use,” which relies entirely on mOPV2 for all serotype 2 responses. Results show that while all scenarios reduce cVDPV2 incidence compared to no intervention, only those incorporating tOPV achieve meaningful reductions in WPV1 cases.
Notably, switching from mOPV2 to tOPV significantly lowers expected WPV1 cases—by up to 438 in Pakistan and 68 in Afghanistan—compared to the base case. This is because tOPV provides concurrent protection against serotypes 1 and 2, increasing overall population immunity without requiring additional campaign rounds. In contrast, continued reliance on mOPV2 maintains a risk of viral reversion and sustained transmission, especially in areas with low vaccine coverage.83-46-5 Molecular Weight Furthermore, the model indicates that targeting only the under-vaccinated subpopulation with tOPV is insufficient to prevent outbreaks, as it fails to halt community-level transmission.204255-11-8 supplier
The findings highlight a critical trade-off: while mOPV2 may offer short-term precision in controlling cVDPV2, its long-term risks outweigh benefits.PMID:25905362 Using tOPV allows for broader, more sustainable immunity and reduces the likelihood of new cVDPV emergences. It also simplifies logistics, as fewer vaccine types are required during SIAs, reducing supply chain burdens and minimizing errors in cold chain management.
Importantly, the model assumes full resumption of pre-pandemic SIA activities by January 2021. If real-world performance falls short—due to ongoing access issues, mobility restrictions, or declining public trust—the projected benefits of tOPV would diminish. Thus, vaccine choice must be coupled with improvements in campaign quality, community engagement, and surveillance.
In summary, replacing mOPV2 with tOPV in outbreak response offers substantial advantages for ending both WPV1 and cVDPV2 transmission. It enhances population immunity, reduces the number of required campaigns, and mitigates the risk of vaccine-derived virus emergence. For Pakistan and Afghanistan, this shift represents a vital step toward achieving global polio eradication—provided that operational capacity keeps pace with strategic intent.MedChemExpress (MCE) offers a wide range of high-quality research chemicals and biochemicals (novel life-science reagents, reference compounds and natural compounds) for scientific use. We have professionally experienced and friendly staff to meet your needs. We are a competent and trustworthy partner for your research and scientific projects.Related websites: https://www.medchemexpress.com
