POLIO STRIKES BACK--ERADICATION ENDGAME SURPRISINGLY DIFFICULT

This has been a very mixed year for the global polio eradication campaign.

What the global polio eradication campaign

wants never to happen again

The good news is that two of the three strains of wild poliovirus have been conquered; they no longer exist except in laboratories.

The mixed news is that the remaining wild poliovirus only exists in two countries, Afghanistan and Pakistan. However, the number of cases in both countries, especially in Pakistan, has been higher than in 2018. The two countries suffered 125 cases of polio compared to just 33 last year, 101 of those in Pakistan. In both countries, strife, insecurity and anti-vacccination propaganda and rumors have enabled the virus to hold on.

The bad news is that the number of people--mostly children--sickened by poliovirus that has mutated back to a virulent form from the live-but-attenuated polio vaccine has more than doubled since 2018. This back-mutation only occurs in one person out of an estimated 2.8 million, but since 450 million children are getting the attenuated vaccine every year, a significant number of cases are inevitable as long as the oral vaccine remains in wide use--unless the surrounding population has a very high rate of "herd immunity." There were 241 such cases in 2019 vs. just 104 in 2018.

The solution is complex, but at hand. In part, it depends on the rapid release of an oral vaccine against the type 2 poliovirus, which is expected to be less likely to mutate to a virulent form. You can read about the global polio endgame strategy here. Plans and resources are in place to make this transition, and the intense, decades-long global campaign to wipe out this deadly disease once and for all will succeed, even if not quite as quickly as hoped.

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REA

POLIO ERADICATION--TWO STRAINS GONE, ONE TO GO

The three-decade-long campaign to eradicate polio--not long ago a worldwide scourge--passed an important milestone this month. The Global Polio Eradication Initiative (GPEI) announced the eradication of wild poliovirus type 3 (WPV3). Type 2 was declared eradicated in 2015. That leaves only one type of wild polivirus, WPV1, still in circulation.

 Somali child receiving an injection of inactivated poliovirus

Credit: PV2 Andrew W. McGalliard

Public Domain

That good news is augmented by the fact that WPV1 only exists in two countries, Afghanistan and Pakistan. This allows resources to be focused on those last two remaining reservoirs of the deadly virus.

However, the goal of finally eradicating polio remains elusive. There have been more cases of wild-virus-caused polio in those two countries (18 and 76 respectively) this year than in 2018. And, there have been a significant number of cases caused when the weakened virus used for oral inoculation mutates back to a disease-causing form. Although very rare, when millions of children are given the oral vaccine, mutation back to a virulent form is enough to keep the disease alive.

To address this problem, GPEI has now shifted into its Polio Endgame Strategy. This is a multifaceted campaign involving continued mass inoculations, rapid response teams to quickly contain and snuff out any flareups, and a shift from oral live attenuated immunization to inoculation by injection of completely inactivated virus. The endgame campaign is estimated to cost $4.2 billion and take four years. If it succeeds, humanity will have eliminated a second deadly disease (smallpox was the first) and no child will ever again be killed or paralyzed by polio.

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You can read an executive summary of the endgame strategy here.