Eradicating Polio

Stephen DeAngelis

January 02, 2008

American’s of my generation and younger don’t really remember the fear of contracting polio that gripped much of the country before the early 1960s. That’s because the disease was pretty much eradicated by vaccines developed by Jonas Salk (given by injection) and Albert Sabin (given orally). Polio was the disease that crippled President Franklin D. Roosevelt and left children with withered limbs or in iron lungs if it didn’t kill them. There has been a push over the last two decades to eradicate polio globally; spurred on by the success of the eradication of smallpox in the late 1970s. Eradicating polio, however, has not proven so easy [“Effort to Defeat Polio Faces Unique Challenges,” by David Brown, Washington Post, 25 December 2007].

“The troubled 19-year-old campaign to eradicate polio is celebrating recent progress and an unexpected infusion of cash, but experts are coming to realize that they will not be able to end the expensive and laborious efforts to control the virus anytime soon. Ridding the world of polio will be a far messier business than the 1977 eradication of smallpox, which remains a unique achievement in medicine. That is because it is now clear that the virus that causes polio could reemerge years, and possibly even decades, after the last case is found. The reason involves peculiarities of poliovirus and the oral (Sabin) vaccine being used to eradicate the disease. The vaccine contains a weakened poliovirus that stimulates immunity against the ‘wild’ virus, which can cause paralysis. On rare occasions, however, the vaccine virus can mutate to a more dangerous form, spread from person to person and cause a paralytic infection. This phenomenon, only recognized in the past decade, has caused outbreaks in 10 countries since 2000. [In 2007], 7 percent of all polio cases worldwide were caused by mutant, vaccine-derived virus.”

Medical researchers working on challenges from HIV to the so-called “superbugs” all must wrestle with mutations and they often remain one-step behind. The medical world is now debating what to do next in fighting polio.

“The only way to prevent [infections from mutant viruses] from happening is to keep the world’s infants and toddlers fully immunized — in other words, to keep up the exhausting, expensive full-court press that has now gone on seven years longer than was anticipated. To rid the planet of polio, people will eventually have to stop using the oral vaccine. Whether they should forgo immunization altogether or use the alternative vaccine — the Salk ‘polio shot’ that does not contain live virus and cannot cause infection — is now under debate.”

That sounds like an easy solution, but it’s not.

“Switching to the Salk vaccine, however, will be hard. It’s more expensive: roughly $2.70 per dose, compared with 15 cents for the oral vaccine. About 135 million infants are born each year, and each will need at least two shots. While the two companies that make most of the world’s supply can ramp up production to that level, it will take them at least five years, and possibly a lot longer. Consequently, even after eradication, many countries will have to continue using the oral vaccine — and be prepared to play a global version of whack-a-mole, spotting and suppressing mini-epidemics caused by it.”

It must be frustrating for those seeking to eradicate polio to be so tantalizing close and yet have to watch the goal continue to move into the future. It’s like one of those scenes from a movie where a man runs down a hall only to see it stretch endlessly out before him. No matter how fast he runs the end of the hall continues to recede.

“This all adds up to an outcome nobody anticipated in 1988 when the World Health Organization, emboldened by the smallpox success, took on polio. ‘My major concern has been that the eradication of wild virus may not be the whole problem in terms of eliminating the disease, or even protecting the world from it,’ said Ellie Ehrenfeld, a virologist at the National Institutes of Health and an adviser to WHO. Before the eradication campaign began, polio paralyzed more than 350,000 people a year in 125 countries. Stopping that suffering is the chief goal of eradication. Health officials also hoped the end of polio would also mean the end of polio vaccination, with its trouble and expense. That was the case with smallpox. No country routinely vaccinates against that disease anymore, a move that has saved more than $17 billion in the United States alone. But an unambiguous transition to a ‘polio-free’ world is unlikely. It will be hard to know when, if ever, it is safe to forgo vaccination.”

Because the smallpox pathogen was so virulent, samples of it were carefully secured and tracked. That is not the case for the polio virus.

“Work is underway to identify laboratories holding poliovirus, reduce their number and increase their security. But unlike with smallpox, there may be places that have the pathogen and do not know it. Poliovirus replicates in the intestine. Thousands of labs around the world have frozen samples of feces that may contain the virus — either the wild type or the vaccine virus — that could theoretically escape. Further complicating matters is the fact that most polio cases are ‘silent.’ In only 1 in 200 infections from the wild virus is there the characteristic muscle weakness that lets physicians make the diagnosis. Polio virus can travel far before anyone knows it. ‘There is going to be a period — and perhaps indefinitely — where the world is going to want that umbrella of protection,’ said Stephen L. Cochi, a physician at the U.S. Centers for Disease Control and Prevention who chairs a committee advising WHO on polio eradication. ‘I don’t think we will ever stop using inactivated polio vaccine’ in the United States, said Walter Orenstein, associate director of the Emory Vaccine Center in Atlanta and an adviser to WHO.”

Another challenge facing the eradication is ignorance and rumor. In an age of conspiracy theories, when so many people believe that governments deliberately lie and betray them, any plausible rumor is accepted as true.

“The campaign threatened to unravel in 2003 when several populous, largely Muslim states of northern Nigeria stopped immunizing because of rumors that the polio vaccine contained the AIDS virus or an antifertility drug. The disease roared back. By the time vaccination resumed a year later, the virus was out of the barn. Over the next three years, 20 countries were reinfected with virus traced via genetic fingerprinting to strains from northern Nigeria. (Seven other polio-free countries were reinfected at the same time after a resurgence of the disease in India.) These included not only many African countries but also such faraway places as Saudi Arabia and Indonesia. Worldwide, polio’s annual toll, which had fallen to 784 in 2003, climbed to 2,000 last year.”

The fact that disease can quickly travel around the world is one aspect of globalization that is double-edged. When the disease can move “silently” like polio, it makes the challenges faced by the medical world all the more difficult.

“Responding to the Nigerian outbreak took hundreds of millions of dollars and a huge amount of work. The main tool in eradication is National Immunization Day, a coordinated effort in which workers go door to door over one or two days and put drops of vaccine in the mouths of every child under age 5. Some reinfected countries had to hold four or five of these days in a year, rather than just two, to become polio-free once more. (Outbreaks
caused by vaccine-derived virus are handled the same way.) … In the northern Indian states of Uttar Pradesh and Bihar, which have a combined population of 270 million, polio is holding on tenaciously. Many people there live in crowded, unsanitary conditions ideal for transmitting the virus. In fact, there are so many intestinal viruses, and so much diarrhea, that the vaccine has a hard time elbowing its way in to get the attention of the immune system. Astonishingly, one-third of polio cases in northern India last year were in children who had gotten the vaccine at least 10 times and still had not developed immunity. “

All this sounds very frustrating (and it is), but the effort is not futile.

“The effort is paying off. The number of reinfected countries is down to seven, and the number of countries where the disease is still ‘endemic,’ meaning it has never been stopped, is now four, the lowest in history. (They are Nigeria, India, Afghanistan, and Pakistan.) Through [at last count], only 857 cases of the disease had occurred [in 2007].”

To address the problem of immunity resistance, like the one described above that has been discovered in northern India, a new tack is being taken.

“Polio campaigners recently switched to a vaccine with only one type of polio virus in it. (Normally, there are three.) This cuts down on the competition and targets the specific type of wild virus in the area. The campaign is gaining traction. ‘We are deep into the high season for transmission and the numbers are still dropping,’ said R. Bruce Aylward, a Canadian physician who directs the eradication initiative at WHO. ‘That is a mix you don’t see very often, and you are seeing it this year.'”

Brown reports that the eradication campaign has now overshot it target date by eight years — with no new target date in sight. Rotary Club International and the Bill & Melinda Gates foundation have teamed to inject another $200 million into the effort (which, according to Brown) has already cost $5.3 billion. With global the global number of cases now under 1000, it is understandable why the push to eradicate the disease has gained momentum. The challenge will be sustaining the enthusiasm long enough to ensure that latent cases don’t develop. Let’s hope the numbers continue to fall in 2008.