Reasons Why Polio Hasn't Been Eradicated

Two polio drops of safety
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Polio isn't over. In fact, the disease is not just back—it never left. Polio can spread unnoticed, allowing us to think we've conquered the illness. The disease can then pop up and prove us wrong.

In the summer of 2016, Nigeria joined Pakistan and Afghanistan as the only three counties where polio is known to still spread. 

What Is Polio?

The virus that causes polio is an enterovirus. The virus spreads fecal-orally (from stool to mouth). This can happen when a bit of stool from an infected person ends up in someone else's drinking water. Not all water is perfectly clean. It can also come from contaminated food. It can also be spread oral-orally, through infected saliva.

The disease results in paralysis in rare cases. This paralysis is acute, meaning that it happens fast. It is also flaccid, meaning that it causes limp weakness, with decreased muscle tone and reduced or absent reflexes. The paralysis can be permanent and there is no cure.

Paralysis occurs in less than 1% of polio cases (about 1 in 200 people who are infected).

Small children who contract polio are most likely to develop paralysis. Of those who are paralyzed, 5-10% may die due to paralyzed muscles that prevent breathing.

In most cases, those who are exposed to the virus have no symptoms. According to the CDC, 72 in 100 who get affected have no symptoms. About 25 in 100 will have mild symptoms that go away in a few days on their own.

Symptoms include fever, sore throat, nausea, fatigue, headache, stomach pain. Of the remaining 3 in 100, some will have pins and needles or a feeling of weakness; some will have inflammation of the meninges that surrounds their brain, called meningitis. 

Overall, most who are infected will never know they had it. But, no one looking for the virus will realize these people were infected either. Polio is a disease we are close to eradicating.

What's so Hard About Stopping Polio?

Preventing polio is all about finding cases, stopping transmission by providing clean water and sanitation, and protecting the uninfected (vaccination). Where one of these fails, the others are needed even more.

Unfortunately, however, it's hardest to vaccinate and provide surveillance where there aren't strong sanitation and water services.

  • Surveillance is hardest where it is needed the most. It is difficult to access areas with insecurity, crowding, lack of sanitation services and clean water. These are the areas where polio is most likely to spread.
  • Vaccination is hardest where it is needed the most. Areas that are vulnerable due to lack of security and poverty are often the areas where vaccination is needed the most. Vaccination is most needed among those who have the least.
  • Surveillance is imperfect. Surveillance can only identify those cases with paralysis. Most cases of paralysis (even acute, flaccid paralysis) will not be due to polio when there isn't an outbreak. Most cases of polio do not result in paralysis, either. So surveillance will turn up many cases that aren't polio and won't begin to identify all cases of polio infection.

What Happened in Nigeria?

It was supposed to be the second anniversary of Nigeria (and hence Africa) being wildtype polio-free. Instead, two cases of wildtype polio were identified in Borno state in Northern Nigeria. Polio was identified in two separate areas of Borno state. Those in these areas did not have contact with each other.

Polio infected one child with what's called acute flaccid paralysis (AFP) in Borno in mid-July. The virus was also found in close healthy contacts of that child. In addition, a related wildtype virus was identified in another in the close (and healthy) contact of a child who had developed AFP symptoms a week earlier in July elsewhere in the state.

What's the Story in Nigeria?

Context always matters with infectious diseases. Polio often strikes where people are the most vulnerable. This is where it can spread.

Boko Haram, a terrorist group, has led to many people not having access to the health services they need. Boko Haram has been one of the deadliest terrorist groups in the world. This adds to the harm caused.

These cases were identified at a time when an estimated 2.5 million people have been displaced in (or around) the Northeast of Nigeria due to insecurity related to the terrorist group, Boko Haram. Many have sought refuge in Borno's capital, which doubled in size. There were roads that were considered too dangerous to drive on; markets that were closed. Most (90%) live outside of formal camps. 

As Boko Haram has been pushed back this summer through Nigerian military operations, these roads could be used and new areas reached. Aid groups and the military going into these previously inaccessible areas saw a lot of people who were very hungry and malnourished. They needed clean water and other services. These were all urgent needs that needed immediate assistance, which the government and aid groups began to supply.

It's Hard to Look for Polio Where It's Most Likely to Be 

Surveillance for Acute Flaccid Paralysis (AFP) then had not been a priority over the past few years in inaccessible areas. These were places where the immediate concerns were for food, safety, and clean water.

Most cases of polio infection will not lead to paralysis (only about 4-5% get sick, less than 1% overall will become paralyzed ).

AFP surveillance, itself, is only an incomplete means of surveillance. Likewise, most cases of AFP are due to something other than polio (outside of an outbreak, that is). AFP should be reported even when there are no cases of polio, as there will be non-polio cases.

What Do We Know About the Virus Found?

The virus is related to the virus that was in Nigeria five years ago.

It's WPV1 (Wildtype poliovirus 1) — but so are all cases in the world. Nigeria last had WPV1 identified in 2014 elsewhere in Northern Nigeria. WPV1 was last identified in Borno in a patient in 2012.

What’s interesting about the WPV1 strains isolated now in Nigeria is that they are closely tied to the strain from 2011. This means for the last 5 years, wildtype polio has likely been in Africa without it being seen.

Is This a Big Setback in the Fight Against Polio?

Any new case is a setback. Any country newly having a case is a setback. Any continent newly having a case is a setback. In this case, there was a new case in a new country, on a new continent. Nigeria and Africa had reached almost 2 years without a case.

To put this set-back in perspective, there has been considerable progress in eradicating polio. The other two WPV strains have not been seen on this planet in years.

WPV3 was last seen in November 2012 in elsewhere in Nigeria. WPV2 was last seen in 1999 in India and was declared eradicated in 2016; the live attenuated type 2 strain is set to be removed, accordingly, from the OPV (Oral Polio Vaccine) which contains live attenuated viruses unlike the injected IPV (Inactivated Polio Vaccine).

The vaccine virus type 2 is to be removed worldwide from OPV because:

  1. The 3 strains in the vaccine individually match the 3 wildtype strains
  2. There is no longer a need for protection against the eradicated WPV2
  3. Removal of live attenuated type 2 virus can reduce the long-term risk of outbreaks of Circulating Vaccine-Derived Polio Virus type 2 (cVDPV2), which has occurred in Nigeria in the past and is the most common cVDPV outbreak strain and
  4. To maintain immunity in high-risk communities, IPV can be administered for VDPV2 protection as well.

It should be noted that the risk of the weakened virus (or a related virus) has been outweighed by the benefits of the OPV and the risks of the separate, unattenuated wildtype virus.

There May Be More

Moreover, if there are gaps in water and sanitation, there remains a risk of polio exposure through the water. Polio is spread "fecal-oral". This can include spread through water.

In Borno, some surveillance has shown in the past some circulating vaccine-derived polio vaccines (cVDPV)’s. Borno had environmental isolation of vaccine-derived Poliovirus (type 2) in April, which is not surprising. However, it was the first time this strain was seen since the vaccine was switched to not include this strain in 2016. This led to the authorization of monovalent OPV2 vaccine in Nigeria from the global stockpile.

Despite interruptions and incomplete vaccination coverage, no one has been reported to have a case of cVDPV in 2016. Such cases can be seen when vaccination rates are low in the absence of wildtype cases, as Lao, Ukraine, Guinea/Mali, Madagascar, and Myanmar have seen since 2015. Borno saw at least a dozen cases of cVDPV in 2014 and at least one case in 2015. So it will be interesting to look out for VDPV cases and see how this will shape the coming response.

Is Progress Being Made?

In 2013, 256 wild type cases were identified in these 3 countries — and 5 others (Somalia, Syria, Ethiopia, Kenya, and Cameroon). In 2014, there were 359 wild type cases, but only 19 were found in countries outside of the 3 endemic countries (Somalia, Ethiopia, Cameroon, Equatorial Guinea, Iraq, Syria). 

By 2015, there were 74 cases, only in endemic countries; none were found outside of Afghanistan and Pakistan. Even better, there may just be one wild type strain still circulating on the planet. 

Type 2 poliovirus no longer exists in the "wild". The last case was seen in 1999 in India. It has been declared eradicated. Type 3 poliovirus (WPV3) may also be gone from the "wild". The last wild type case of WPV3 was seen in 2012 in Pakistan. The most recent wild type cases have all been type 1 (WPV1).

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