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Polio Endgame Issues

Monday, 10th of September 2012

 

• POLIO ENDGAME ISSUES

 

Excerpt below; full text is at http://www.who.int/bulletin/volumes/90/7/BLT.12.020712.pdf

WHO Director-General Dr Mar­garet Chan told the [World Health] Assembly that polio eradication was “at a tipping point be­tween success and failure,” highlighting the funding gap of US$ 945 million until the end of 2013 (against a US$ 2.19 billion budget for that period). This year alone, the cash shortage has led to a reduc­tion in mass vaccination activities in 24 high-risk countries, putting millions of children at risk.

The polio eradication endgame plan is to switch from the trivalent oral polio vaccine, currently the vaccine of choice in most countries, to two vaccines: a new bivalent oral polio vaccine for routine immunization backed up by judicious use of inactivated polio vaccine (IPV).

First used in Afghanistan in 2009, the bivalent oral polio vaccine is at least 30% more effective than the old trivalent oral polio vaccine against polioviruses types 1 and 3 and does not contain live type 2 poliovirus that caused most of the outbreaks of circulating vaccine-derived poliovirus since the first outbreak in Hispaniola.

Bivalent vaccines protect against two serotypes of a disease, trivalent vaccines against three. In the case of polio, although there are three types of the poliovirus, it is the type 2 compo­nent in the trivalent oral polio vaccine has caused more than 80% of cases of vaccine-derived polioviruses that have caused outbreaks and so removing the type 2 component from the vaccine is vital to success.

And that is where IPV comes in. IPV, which is administered through injection, provides immunity to all three types of poliovirus but, unlike the oral vaccine, does not cause vaccine-derived polio because the virus used in its manu­facture is dead.

Unlike the oral vaccine, however, IPV does not invoke intestinal immunity needed to stop transmission. So a child who receives only IPV won’t develop polio, but could excrete the virus per­petuating its circulation. That’s why a combination of both the bivalent oral vaccine and IPV is now necessary.

“IPV would serve as a kind of in­surance policy by boosting children’s immunity to type 2 and would have the added advantage of also boosting types 1 and 3 immunity and, thereby, ac­celerating the removal of those last wild polioviruses,” says WHO’s Roland Sutter, coordinator of the Research and Product Development Team of the Global Polio Eradication Initiative.

This two-prong strategy, involving the bivalent oral polio vaccine and IPV, Aylward and Sutter believe, will succeed in eliminating the main risk due to the type 2 virus. After the eradication of all remaining strains of wild poliovirus transmission, countries could stop using the bivalent oral polio vaccine, eliminat­ing any residual remaining risks associ­ated with the type 1 and 3 components contained in that vaccine.

The chief hurdle to this plan is cost. At a minimum of US$ 3 a dose, IPV is far too costly for the low-income countries that might need it most. So the fear when developing the plan was that, in the unlikely event that a type 2 vaccine-derived poliovirus did emerge during or immediately after the switch, children with immunity only to types 1 and 3 wouldn’t be protected as countries would not be able to afford IPV.

The challenge, then, was to find a way to use IPV in a significantly less expensive but yet sufficiently effective way. And Aylward knew that wouldn’t be easy. “If you’re a manufacturer, there isn’t a great incentive to find ways to make your product more cheaply available,” he says. “We sometimes had to push hard.”

Eventually, in 2010, WHO experts collaborated with researchers in Cuba and Oman, among other countries, to look at four possible scenarios to reduce the cost of IPV use: reducing the number of doses, using a fractional (1/5th) dose, increasing the interval between doses and producing the vaccine in resource-limited settings. “All of this work was driven by a developing country need for a cheap solution to this circulating vaccine-derived poliovirus problem”, says Aylward, “and the really exciting thing is that most of this research took place in developing countries.”

Moreover, he says, the results were far better than expected. “Will one-fifth of a dose work?” he says. “Yes, just as well as a full dose for boosting. Will two doses work as well as four doses? Yes, if you give them four months apart. Can you make an affordable IPV product in a low-income country? Well, it turns out you probably can. These were all big surprises for many working in im­munization.”

“What we need now is for manufac­turers to agree to produce intra-dermal fractional dose IPV, and for licensing bodies to rapidly examine whether this potential solution can undergo fast-track licensing – given the strong public health imperative – so that we have it within a year,” says Aylward. But for all of the promising data, that has yet to happen.

“The A380 is on the runway, but we haven’t gotten it up in the air yet. And that requires a lot of people cooperating.”