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Polio eradication within reach
Wild polio virus cases have declined considerably since the 1988 World Health Assembly resolution to eradicate polio, and the final goal appears within reach, according to a recent literature review published in Future Microbiology.
“Poliovirus transmission has been wiped out from more than 99% of the world with the successful use of OPV [live attenuated oral polio vaccine] and IPV [inactivated polio vaccine] over the past several decades,” Ananda S. Bandyopadhyay, MPH, of the Bill and Melinda Gates Foundation, and colleagues wrote.
“However, to maintain a world permanently free from the risk of all polioviruses, the eradication program will have to overcome challenges such as the rare occurrence of revertant neurovirulent and highly transmissible strains of polioviruses from OPV.”
Ananda S. Bandyopadhyay
The Global Polio Eradication Initiative has developed the Polio Eradication and Endgame Strategic Plan that aims to wipe out the last cases of polio from all causes by 2018, the researchers wrote. Cases of wild polio virus-related paralysis have decreased from 350,000 in 1988 to 359 in 2014, and only Pakistan, Nigeria and Afghanistan are currently considered endemic for polio.
Both OPV and IPV work well against polio in most situations, the researchers wrote, but each comes with a major caveat. OPV causes paralysis in approximately five cases per 1 million births due to vaccine-associated paralytic poliomyelitis, leading most developed nations to transition to IPV. However, IPV does not provide the same level of intestinal immunity that OPV does, a problem in countries where fecal-oral transmission of polio is an issue.
“The Strategic Advisory Group of Experts recommends all OPV-using countries introduce at least one dose of IPV into the routine administration schedule before the end of 2015 in order to provide a poliovirus type 2 immunity base prior to and after the global switch from trivalent OPV to bivalent OPV,” the researchers wrote. “[Adding this dose of IPV will] reduce risks associated with OPV2 cessation; facilitate interruption of transmission with the use of monovalent OPV2 if type 2 outbreaks occur; and boost immunity against types 1 and 3, thus hastening polio eradication.”
The researchers said using both IPV and OPV would be ideal, but carries a considerable cost. OPV alone is often the choice in developing countries in part because it is much less expensive per dose (15 cents vs. $1 or more). However, the researchers said it is necessary to invest a projected $5.5 billion in order to take polio eradication efforts to the next level.
“Because OPV can rarely cause paralysis and generate revertant polio strains, IPV will have to replace OPV after eradication of wild polio virus is certified to sustain eradication of all polioviruses,” the researchers wrote. “Although substantial effectiveness and safety data exist on the use and delivery of OPV and IPV, several new research initiatives are currently under way to fill specific knowledge gaps to inform future vaccination policies that would assure polio is eradicated and eradication in maintained.” – by David Jwanier
Disclosure: Bandyopadhyay is an employee of the Bill and Melinda Gates Foundation. Please see the full study for a list of all other authors’ relevant financial disclosures.