Oral vaccine key defence against polio but also behind detection of vaccine-derived poliovirus in wastewater samples
An increase in wild poliovirus cases in 2022 shows the fragility of the fight against the highly infectious viral disease, said a commentary published in BMJ Global Health journal in December. It also shows the importance of continued efforts to capitalise on the advances to finally eradicate it, while taking steps to ensure the world remains polio-free post-eradication.
In 2022, several countries like Canada, the United States, the United Kingdom and India reported wastewater samples testing positive for vaccine-derived polio. Until November 2022, some 30 cases of wild polio virus were detected. In comparison, 2021 saw just six cases and 2020 saw 140.
Canada reported two samples of vaccine-derived poliovirus in their wastewater December 23, 2022. the samples were collected in August 2022. Investigations are underway to assess any genetic linkages to the polio cases detected in New York State last summer.
Read more: WHO report flags spike in cases of vaccine-derived poliovirus
Last year also saw wastewater samples testing positive for vaccine-derived polio in London and Kolkata.
Of the 30 cases of wild poliovirus, most came from Pakistan and some countries in east Africa, which were declared wild polio-free in 2020. Currently, Pakistan and Afghanistan are the two endemic countries for the virus.
The oral polio vaccine (OPV) is the key defence against the viral disease. Still, it is also the reason behind the detection of vaccine-derived poliovirus in wastewater samples.
This is so because a live attenuated vaccine virus in OPV can lead to paralysis in approximately two to four events per million births, according to the World Health Organization (WHO).
In communities with low vaccination coverage, the vaccine virus can circulate, mutate and become neurovirulent — the ability to infect the nervous system — again, the global health body noted.
However, the advantages of OPV outweigh its disadvantages as it is cheap, accessible and effective, making it the primary tool in the fight to eradicate polio.
Read more: Polio virus in sewage sample again: This time in UK
WHO’s Global Polio Eradication Initiative (GPEI) strategy 2022–2026 has a two-pronged approach. The first is eradicating wild poliovirus by ramping up all vaccination routes.
Once wild polio has been eradicated globally, the WHO recommended route is to phase out OPV to tackle vaccine-derived poliovirus and shift focus towards inactivated polio vaccine (IPV) for the following decade.
The commentary cited a modelling exercise conducted by a WHO programme, Routine Immunisation to Secure Eradication, on the estimated demand and supply for IPV once countries implement the global health body’s guidelines. A serious shortage was noted unless investment is strengthened.
This is critical since the second phase of eradication will rely exclusively on IPV. “However, the polio vaccine market is unpredictable given polio will be only the second human disease ever to be eradicated (smallpox was the first) and the only one to have continued immunisation for another decade,” the authors argued.
An IPV shortage has occurred in the past, once in 2017 and again the following year. Conception to the production of IPV vaccines takes an estimated five to seven years. In comparison, procurement plans of governments, groups of governments or international organisations are typically for around two-three years, the article noted.
“None procure far enough in advance or with firm enough commitments to generate the investment required now. This means there is no clear certainty of demand for manufacturers making,” the BMJ article noted.
Read more: Vaccine-derived polio virus found 50 times in India in six years
The authors suggest a possible solution; an advance volume guarantee, where “a group of donors would assure a guaranteed, multi-year purchase of a minimum number of doses at a price derived from publicly available international agreements with international purchasers.”
If the supply outweighs the demand, a pay-out mechanism will kick in for the donors.
“Given the current progress in eliminating wild poliovirus, eradication is likely to happen sooner than thought possible a few years ago. Demand for IPV-containing hexavalent vaccines is likely to increase well beyond manufacturers’ ability to respond based on their current investments, but they will not invest more unless that demand is guaranteed,” the authors said in conclusion.
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