WHO’s database on polio cases hides more than it reveals

On June 17, 2022, WHO published a report of a VDPV type-1 case that was detected from an environmental sewage sample in Kolkata on April 25, 2022. The report said that genetic sequencing “established that it was not related to any of the previously identified VDPV1 viruses and was likely to be iVDPV (excreted from an immune-deficient individual)”. But nearly three months after the results of the Meghalaya polio case was shared with the WHO on August 12, and more than one-a-half-months after the follow-up results confirmed that the immunological profile of the child was normal and that there was no evidence that the virus was circulating in the community, WHO is yet to publish the details.

If the failure or delay by WHO in publishing the case details is puzzling, it has now come to light that besides not reporting vaccine-associated paralytic polio (VAPP) cases, the WHO registry does not report all categories of vaccine-derived poliovirus (VDPV) cases either. WHO classifies VDPV cases into: 1) circulating vaccine-derived polioviruses (cVDPVs), 2) immune-deficiency associated VDPV (iVDPV), and 3) ambiguous vaccine-derived polioviruses (aVDPVs). However, besides wild poliovirus cases, the WHO registry has data of only the circulating VDPV cases and not the cases that belong to the other two categories — iVDPV and aVDPV. In fact, the registry does not even list the other two VDPV categories, namely the iVDPV and ambiguous VDPV. Even in the case of the circulating VDPV cases, the WHO registry does not classify the cases based on poliovirus serotypes — type-1, type-2 or type-3. 

Like the WHO registry, the registry maintained by the Global Polio Eradication Initiative (GPEI), which is a public-private partnership led by national governments with six partners, including the WHO, also has data on only the circulating VDPVs and not the other two VDPV categories — immune-deficiency associated VDPV and ambiguous VDPV.

In the case of the wild poliovirus, the GPEI registry has data of confirmed human cases and environmental samples. In the case of the circulating VDPV cases too, in addition to circulating VDPV cases, the GPEI registry has data of environmental samples and other human sources that include contacts, healthy and community samples. Also, the GPEI database classifies the circulating VDPV cases as type-1, type-2 and type-3. However, while the WHO registry provides data of circulating VDPV cases globally and individual countries starting from 2000, the GPEI database has data of circulating VDPV cases and environmental samples of individual countries only for the last four years — 2021 to 2024. In the case of the wild poliovirus cases, the GEPI database has data only for the last seven years — 2018 to 2024.

As per a 2017 paper published in the journal Vaccine, the GPEI maintains a registry of iVDPV cases. However, the data of iVDPV cases in the GPEI registry is not made publicly available. Instead, the GPEI periodically publishes a list of iVDPV cases in the World Epidemiological Record (WER) and the U.S. CDC’s Morbidity and Mortality Weekly Report (MMWR). The last time GPEI shared the data of iVDPV cases was in July 2020 when 16 new iVDPV cases were reported from five countries — Argentina, Egypt, Iran, Philippines, and Tunisia — between July 2018 and December 2019. 

If GPEI has the data of all iVDPV cases, the WHO too should have the same data as all the WHO-accredited polio laboratories, which confirm both wild poliovirus and VDPV cases and classifies the VDPV cases into one of the three categories, report the results directly to the WHO. This raises important questions about WHO’s intent and its unwillingness to be transparent by sharing the data of immune-deficiency associated VDPV (iVDPV), and ambiguous VDPV cases on a real-time basis.

Unlike in the case of the inactivated polio vaccine (IPV), the oral polio vaccine (OPV) can sometimes cause polio. Instead of protecting the vaccinated children, OPV can sometimes cause polio —vaccine-associated paralytic poliomyelitis (VAPP) — in children who are vaccinated. This occurs when the live, weakened poliovirus used in OPV turns virulent within the body of the recently vaccinated child and causes polio. The live, weakened poliovirus used in OPV can also sometimes turn neurovirulent and cause polio in children who are not fully protected, and in children who are not immunocompetent. In the case of iVDPV, poliovirus can continue to replicate in an immunodeficient child and the iVDPV strain can be excreted for several months to years. In one case, an immunodeficient child was found excreting type-2 VDPV for 28 years.

“The risks posed by iVDPV strains and the prevalence of such cases globally are unknown so their relevance in the context of the GPEI endgame is not easy to assess,” says the 2015 PLOS Pathogens paper. WHO is well aware that iVDPV cases serve as potential reservoirs for neurovirulent VDPV strains and can pose a significant threat to the eradication campaign. This precisely is the reason why WHO does not share the data on iVDPV cases.