Heightened awareness, renewed commitment needed to eradicate polio

Fears about vaccination, political unrest and global financial crisis threaten 20 years of progress.

Since the world’s top health and humanitarian organizations first joined forces in 1988 to eradicate polio by the year 2000, the number of polio endemic countries has shrunk from 125 to four and the number of cases per year now equals what was once a daily average. And yet, polio continues to threaten the health of people around the world.

Importations from endemic countries during the past five years have led to reemergence of the disease in several African and Asian countries that were once declared polio-free. Health officials are currently struggling to stamp out a 15-country outbreak in Africa.

“Such large-scale polio outbreaks haven’t been seen in quite a long time,” Tammam Aloudat, MD, MPH, senior officer in health emergencies at the International Federation of Red Cross and Red Crescent Societies, told Infectious Disease News.

The current polio resurgence can be traced back to 2003 when rumors circulated in Nigeria that the oral polio vaccine used to immunize children would spread HIV and sterilize young girls. After political leaders endorsed the rumors, vaccination programs in the country came to a halt for 11 months.

By 2006, polio strains originating from Nigeria had spread to 20 previously polio-free countries in both Africa and Asia, resulting in more than 5,000 cases of paralytic polio. At the end of 2007, vaccination campaigns contained polio transmission caused by importations in all of the affected African countries except Angola, Chad, the Democratic Republic of Congo, Niger and Sudan. During the past year, however, an additional 32 wild poliovirus (WPV) importations originating from these countries resulted in the current outbreaks in three regions of Africa.

Uninterrupted WPV transmission continues in northern India, due to reduced oral poliovirus vaccine (OPV) effectiveness, and also in Pakistan and Afghanistan, where conflict prevents people from receiving vaccine.

Health officials agree that as long as virus transmission continues, Western nations are at risk.

“WPV is only a plane ride away from the United States,” said Walter A. Orenstein, MD, deputy director of vaccine-preventable diseases at the Bill & Melinda Gates Foundation and Infectious Disease News Editorial Board member. “If we let down our guard, if our immunization coverage drops, there is certainly the possibility of a polio outbreak.”

In an interview, Steven L. Cochi, MD, MPH, senior advisor in the CDC’s Global Immunization Division, said, “Every country is vulnerable as long as any country is not adequately implementing the proven strategies that will eradicate polio.”

Risk for U.S. importation

Although the United States has not had any domestically acquired paralytic WPV cases since 1979, officials emphasize that health care providers and the public must remain alert. Assuring high levels of immunization coverage and considering polio in the differential diagnosis of any patient who presents with acute flaccid paralysis are a physician’s two duties to protect patients against the risk of imported poliovirus, according to Orenstein.

“We know today that nothing is far away. Diseases cross borders so easily,” Aloudat said. “In 2003, severe acute respiratory syndrome jumped from East Asia to Canada in a matter of days. Just a few years ago, polio jumped from the Port of Sudan across the Red Sea and into Gulf countries such as Saudi Arabia and Yemen.”

Current vaccine recommendations in the United States state that children should receive four doses of inactivated poliovirus vaccine (IPV) — with the first dose administered at age 2 months, the second at 4 months, a third at 6 to 18 months and the last at 4 to 6 years.

U.S. polio vaccine coverage levels were high in 2007, with 92.6% of children aged 19 to 35 months having received at least three doses. More than 95% of children were covered in time for school entry, data from the last complete National Immunization Survey indicated.

However, health officials warn that the public can become complacent, particularly about diseases they may have never seen.

“Doctors must be ever vigilant about the possibility of polio and be clear to patients and parents that vaccination must continue to provide a barrier of protection against the possibility of being exposed to an importation of polio from parts of the world where it still exists,” Cochi said.

The other half of prevention is recognition of cases should they occur. Physicians a century ago were more adept at diagnosing polio without help from modern technology.

“Today it would be much harder for us to even suspect the disease in the West,” Aloudat said.

Physicians should consider polio in any child with acute flaccid paralysis who has traveled to an area where WPVs are, Orenstein said. Because only one in 200 cases of polio result in paralysis, it is important to recognize that people can still contract the disease from a person with an asymptomatic infection, Orenstein said, suggesting that if a physician suspects polio, they should contact their state health department immediately to ensure that the proper specimens are collected. The clinical diagnosis of polio is usually confirmed through detection of polio viruses in stool samples.

Easing vaccine anxiety

In Western nations, vaccine anxiety poses the biggest threat to polio eradication efforts as more parents opt out of vaccinating their children. Aloudat called these decisions “extremely unwise and dangerous.”

“This is not a unique phenomenon. In many Western countries with better education and more resources, people believe that vaccines cause autism,” Aloudat said. “Eradicating a disease isn’t only about delivering vaccine. … It’s about delivering a message and helping communities become more aware and better informed.”

At the global level, fostering trust between medical and indigenous communities is one of the Red Cross and Red Crescent Society’s main goals during emergency and routine polio vaccination rounds. Community volunteers play a vital role in the emergency vaccine campaigns in Africa, where volunteers travel door to door sharing life stories and telling families about the polio vaccine. The goal is to reach 25 million of the most remote, children who remain unvaccinated in outbreak-affected countries.

“Our volunteers carry global fundamental principles, approaches and tools, and they take them and adapt them to how their communities think,” Aloudat said. “They deliver simple messages and show by example how global programs can be translated into local activity.”

What’s next in endemic countries?

Although polio vaccine coverage rates remain high in the United States and other Western nations, many areas of the world lag significantly behind WHO’s 2010 goal of 90% global vaccine coverage. Increasing cooperation between health officials and political leaders, and improving vaccine implementation strategies in the remaining endemic countries are major goals.

Nigeria’s polio vaccine coverage remains the lowest of the endemic countries at 61%.

“The main problem in Nigeria is shortcoming in the delivery of the vaccine,” Cochi said. “If we could adequately immunize children with good implementation of strategies, polio would already be gone.”

In 2008, 799 cases of WPV occurred in Nigeria, almost half of the 1,652 cases worldwide last year.

Nigeria’s failure to achieve adequate vaccination rates hinges on issues that go beyond public trust and into the realms of inadequate organization, supervision and accountability at the government level.

“Nigeria has a very decentralized form of government and health care delivery. Getting ownership, particularly in northern states, by political leadership and health officials has been a very slow process,” Cochi said. “But there are signs that is now moving strongly in the right direction.”

In March 2006, Eyitayo Lambo, Nigeria’s federal minister of health, signed the Communiqué of Abuja along with representatives of 10 other African nations, renewing their commitment to meet international health targets including polio eradication.

“Nigerian leadership is taking polio extremely seriously,” Orenstein said. “We are very impressed with the kinds of efforts they’re making now.”

Vaccination rates in Afghanistan and Pakistan are slightly higher than those in Nigeria, at 83% in each country. Lack of security in Taliban-controlled areas — particularly in Kandahar and the southern region of Afghanistan and along the eastern border where Afghanistan meets the northwest frontier province of Pakistan — has resulted in whole groups of children not being vaccinated.

These groups of children can trigger small outbreaks, Cochi explained. Like Nigeria, inadequate vaccine implementation is another factor behind poor coverage in districts where conflicts are not occurring.

But political commitment from Pakistani leaders has improved during the past year, with the president and prime minister creating a polio eradication task force to achieve better vaccine delivery in the few districts still sustaining poliovirus spread, Cochi said.

“The government has committed to work with the World Bank to have a sustained way of financing OPV over the next three years so there won’t be interruptions or shortages in vaccine supply, and there’s more effort to improve supervision and accountability in poor performing districts,” he said.

Reaching conflict areas will depend on negotiations between nongovernmental organizations and the Taliban for cease fires and days of tranquility to achieve the common goal of delivering vaccine to children who need it, according to Cochi.

Suboptimal vaccine efficacy

The vaccine situation in India, the last of the four countries that has never interrupted transmission of WPV, is unique. For unknown reasons, the effectiveness of OPV is reduced, particularly in two northern states, Uttar Pradesh and Bihar, compared with other areas of the world. In addition, polio transmission is facilitated in these areas because of crowded living conditions, poor sanitation and frequent migration.

“We don’t really understand it, but these are the two most populous, poor and crowded states of northern India where we continue to see WPV,” Cochi said.

High incidence of diarrheal illness among children due to poor sanitation also contributes to reduced vaccine efficacy, he explained. Achieving adequate immunity has required administering many more doses of OPV in Indian children than those in other areas of the world.

“Attempts have been made to overcome these shortcomings by using a mono-valent OPV as opposed to the trivalent vaccine,” Cochi said. “Then you remove the competition from the vaccine itself for those three different vaccine viruses to successfully infect the intestinal tract and cause a good immune response.”

A recent case-control study in Uttar Pradesh concluded that trivalent OPV had an effectiveness of 11% per dose against type 1 polio. In contrast, monovalent OPV type 1 had an effectiveness of 30% per dose.

Health officials have been using mono-valent OPV to vaccinate against the two WPV strains still circulating in India, WPV type 1 (WPV1) and WPV type 3. However, officials are stepping up efforts to wipe out WPV1 because of the higher association between this strain and paralysis, as well as its propensity to spread further faster.

“The focus has been on getting rid of the type 1 virus as the priority because that will disproportionately reduce the number and size of polio outbreaks and reduce the risk of spread to other countries and regions of the world,” Cochi said.

Additionally, health officials are discussing the possibility of adding IPV to OPV during mass vaccination campaigns in some of the highest-risk districts of northern India to improve immune responses by taking advantage of both vaccines. At the moment, there are no current plans to implement widespread IPV administration during this pre-eradication phase.

“In northern India, the issue is sustaining good quality immunization rounds with the monovalent vaccines,” Cochi said. “We’re going to be looking very closely to see whether WPV1 survives the low season, and we should know by June or July whether or not we’re successful at snuffing out WPV1 in India.”

Post-polio paradigm shift

The potential for WPVs to reseed the population post eradication (eg, laboratory escapes due to breaks in containment) and the potential for vaccine polio viruses to mutate and rarely take on the transmissibility and virulence characteristics of WPVs (circulating vaccine-derived poliovirus (cVDPV)) and the fact that some immunocompromised people can be chronic shedders of virus that could potentially mutate toward viruses with the phenotypic characteristics of WPVs, have caused many in the health care community to reconsider the Eradication Initiative’s initial goal to cease all vaccination after the last documented case of polio. Continued use of OPV, particularly in populations with low immunization coverage, can lead to circulation of the vaccine viruses, which over time can accumulate the critical mutations to become cVDPVs. Since 2000, at least 11 outbreaks of cVDPV have been detected. Nigeria has had ongoing cVDPV type 2 since 2005 with at least 193 cases.

“Because of the combination of those rare circumstances, I think we’ve altered our thinking about a post-eradication world,” Cochi said. “It seems necessary to be using IPV for at least some period of time following eradication of naturally occurring poliovirus.” This would assure population immunity to prevent spread of both wild viruses, if introduced, or of vaccine viruses, he said.

In March 2009, health officials in Minnesota implicated vaccine-derived poliovirus in the paralysis and death of a woman there. The patient had an inherited immunodeficiency disease, and, based on genetic sequencing, CDC officials believe the infection was latent for more than 10 years.

“It’s not known why it manifested itself at this point and time, but she most likely got the virus from someone who had received the live-attenuated OPV vaccine before its use in the United States was discontinued, possibly from exposure to one of her children,” Cochi said.

Only about 45 cases of chronic infection with a vaccine-derived poliovirus have been documented since the inception of live-attenuated OPV in the United States in the 1960s and all were people with inherited immuno- deficiency diseases.

Vaccine-derived polio from immune deficient people is extremely rare, Cochi said, and depends on people with already-vulnerable immune systems coming in contact with someone who has received oral polio vaccine and is still shedding the virus.

Cochi projects after at least three years of intensive surveillance, efforts to replace OPV with IPV will commence.

The global economy

Slumping economies in many Western nations may have a negative effect on the future of donation-dependent eradication programs, but commitments by several governments and nonprofit organizations suggest that polio programs may weather the economic downturn.

“One thing we’ve been able to accomplish in the Gates Foundation is to leverage our funds. As other groups see that the Gates Foundation is investing heavily, they have also come forward and invested money,” Orenstein said. “So far we’re doing reasonably well with financing.”

Aloudat said that pleas from the International Federation of Red Cross and Red Crescent Societies for emergency vaccine campaign funds are slow to be answered, despite the modesty of recent proposals compared with those in the past.

“Maybe in better economic times we would have fulfilled the money we are requesting within 48 hours because people would be eager to give, but people now are less eager because of internal problems,” Aloudat said.

Both he and Orenstein call for renewed commitment to eradicating the disease. “It would be a terrible tragedy to let polio out of the bag now,” Orenstein said. “We’re so close. We just need to finish the job.

“If we could demonstrate as we did with smallpox that the world can come together against a common enemy and fight that enemy and be successful, we set the stage for solving all sorts of other problems in global health. Polio eradication is a win-win effort for the United States and the world. In the world we prevent this terrible crippling disease, and in the United States we reduce the threat of importation,” Orenstein said. – by Nicole Blazek

For more information:

• CDC. Morb Mortal Wkly Rep. 2009;58(14):357-362.
• Chumakov K. Clin Infect Dis. 2008;47:1587-1592.
• Cochi SL, Kew O. JAMA. 2008;300(7):839-841.
• The World Health Organization. Wkly Epidemiol Rec. 2009;84(14):110-116.