After a successful trial involving nearly two million American children, Jonas Salk’s polio vaccine was found safe and effective in 1955, turning the tide against a highly infectious disease that can cause paralysis or death. Before Salk’s discovery, 25,000–50,000 cases were reported annually in the US, and nothing was known about the virus’s propagation.
Salk’s injectable inactivated polio vaccine (IPV) was formalin-treated. Albert Sabin developed an oral polio vaccine (OPV) using attenuated mutant strains to increase antibody production without triggering the disease. Sabin’s live-virus vaccine, introduced six years later, was cheaper and easier to give than Salk’s and helped eradicate polio worldwide.
That attempt succeeded. Since 1988, when the World Health Assembly issued a resolution to eliminate the disease worldwide and established the Global Polio Eradication Initiative, wild polio infections have dropped by more than 99 percent, from 350,000 to six reported cases in 2021. Wild poliovirus is widespread in Pakistan and Afghanistan. However, two strains have been eradicated. Mass immunization and better sanitation and hygiene contributed to this breakthrough.
Given the rising frequency of vaccine-associated polio cases caused by the live virus, the OPV may be obsolete. Circulating vaccine-derived poliovirus (cVDPV) is rare but rising, with approximately 1,000 occurrences worldwide in 2020. An increase shows that cVDPV hinders polio eradication.
OPVs have advantages. It immunizes the digestive tract, where polio replicates, unlike IPV. Thus, this vaccination increases immunity and prevents transmission, making it useful in locations where the wild poliovirus persists (the IPV protects individuals but does not prevent transmission). The live-vaccine virus in human feces can protect the community in low-sanitation environments.
Community spread can be problematic in low-immunization environments. After a long period of unchecked propagation amongst unvaccinated children, the virus mutates into a paralyzing variant, causing cVDPV infections.
The Covid-19 pandemic halted vaccination campaigns, which increased wild polio and cVDPV cases. Thus, Afghanistan recorded 56 wild polio cases in 2020, up from 29 in 2019. During the second half of the 2020s, Pakistan’s surveillance infrastructure suffered due to heightened polio transmission. Malawi had one wild polio incidence in 2021, while Mozambique had eight in 2022, related to a Pakistani strain.
Even though Africa was proclaimed wild poliovirus-free in 2020, cVDPV cases outweigh wild polio cases, and outbreaks are most common there. Even low-immunization countries like the US, UK, and Israel have them. Due to halted mass immunization campaigns, poor countries with many zero-dose children are at risk.
The pandemic highlighted the difficulties of funding public-health efforts during several crises. In March 2020, the WHO Diverted 60–70% of African polio eradication funds to COVID-19. One estimate suggests that WHO pandemic vaccination guidelines, designed to protect health workers, raised operational expenses by 50% or more.
The Global Polio Eradication Initiative must consider that IPV is five times more expensive than the OPV as it works toward this switchover. The effort should help low-income countries manufacture doses and strengthen vaccine donor-developing world cooperation. It should also examine how the pandemic has damaged vaccine confidence and prioritize vaccination planning and reporting in conflict and disaster zones. This requires donor funds, resources, and assistance.
Sabin’s live-virus vaccine has helped eradicate polio. OPV should be abandoned to eradicate the disease. Vaccine-derived polio, which paralyzed my friend, is rare but growing. We can only conclude by facing it.
