A Safer Polio Vaccine: Will More Stable, Hyper-Attenuated Strains In The Vaccine Be The Death Of Polio?

Since only three out of 10 people infected with poliovirus ever show symptoms and only around 0.5 percent of those infected will be paralyzed, polio can spread through populations unnoticed. Nonetheless, this feared disease may be on its way to global eradication, experts say. Now, the hunt is on to find a safer vaccine that can be used worldwide to ensure polio goes away and stays away.

According to Medical News Today, only Afghanistan and Pakistan still need to end the transmission of polio. The World Health Organization (WHO) calls the fight against polio "the largest-ever internationally coordinated public health effort in history." Reportedly, there are only three wild types of polio and only one type remains today. Experts expect the poliovirus to be completely eradicated in a few years, but say that eradication will present a new challenge: making sure it never comes back.

Post-eradication considerations are crucial. Experts say that stockpiling vaccines that contain live viruses should be re-evaluated. A new study, published in PLOS Pathogens, examines safer vaccine strains that would probably pose less of a threat to humanity if they were somehow accidentally released. Right now, there are two types of polio vaccines. The first contains an inactivated virus and is the vaccine used in places like the United States. The method of producing inactivated poliovirus vaccines carries inherent risks during the production process, because in order to manufacture the IPV, large quantities of live polioviruses have to be grown before being inactivated for use in the vaccine. The second type is the OPV, which contains the live attenuated virus. Live attenuated polioviruses are weakened and are supposed to carry genetic mutations preventing them from infecting anyone. The problem with the OPV, which is commonly used in less industrialized countries and was once used globally, is that they can revert back to their virulent mode. It's not common, but it can happen. Another risk is that with the live attenuated polio vaccine, the virus can lay dormant in a person's system and be shed through the person's feces for decades, possibly transmitting polio to others.

The National Institute for Biological Standards and Control in the U.K. discovered that a British man who was fully vaccinated against polio has been shedding the virus for nearly three decades. Inquisitr covered that story at the time. The man had been vaccinated with the live weakened poliovirus vaccine, but the poliovirus survived in his system. He shed the virus in his stools for decades, and what's worse is that the weakened poliovirus mutated back into a form of polio that can actually cause paralysis. In all those years, the man had no clue that his feces contained a wildly virulent and paralytic strain of polio.


The polio vaccine study most recently published in PLOS Pathogens was conducted by Philip Minor at the National Institute for Biological Standards and Control and considers how we can make safer polio vaccines to be used in the future in order to make sure polio remains eradicated once it's declared eradicated. The team takes the WHO's recommendation to switch to the attenuated Sabin strain, but builds upon it in search for a safer, better vaccine. They actually altered Sabin's RNA trying to create a vaccine that contains more stable, but hyper-attenuated strains. The team claims they have developed what will be the safest polio vaccine in so much as its ability to make sure polio does not come back.

"We have developed new strains for inactivated polio vaccine production with negligible risk to the human population should they escape. [This will] allow for safe vaccine production in the post-eradication world."
Humans have only successfully eradicated two diseases. Smallpox was considered gone forever in 1979 and rinderpest (which affected cattle) was eradicated in 2001. The smallpox vaccine was different in that it used a virus called vaccinia, another pox-type virus that is not smallpox, but was shown to help our bodies develop immunity to smallpox. A person infected with vaccinia is protected against developing small pox.The vaccine against small pox was significantly different than vaccines made by attenuating live viruses or using inactivated viruses, according to the U.S. CDC, because it never contained any version of smallpox and could never spread smallpox even by accident or through viral shedding from vaccines.It makes sense that experts are taking the issue seriously since, the BBC reported, sewage samples "[all] bore the molecular fingerprints of 'iVDPVs' – vaccine-derived polioviruses."

The team explained the purpose of their new study.

"New polio vaccines will be needed to safeguard global eradication: Sabin strains are known to evolve to fill the niche left by wild-strains so their long-term use is incompatible with eradication; most current inactivated vaccine is made from wild polioviruses so that production presents a significant biosecurity risk.We have developed new strains for Inactivated Polio Vaccine (IPV) production with negligible risk to the human population should they escape."
The team stated they believe they have finally constructed polioviruses to be used in a new vaccine that are extremely attenuated and genetically stable in cell culture.

On Friday, The Express Tribune with the International New York Times in Pakistan reported that a government inquiry found that polio vaccines given to infants that were funded by the Global Alliance for Vaccination and Immunisation are causing deaths and disabilities in Pakistan. The report on the alleged polio vaccine deaths was prepared by the Prime Minister's Inspection Commission (PMIC) and recommends that "Prime Minister Yousaf Raza Gilani immediately suspend the administration of all types of vaccines funded by the GAVI."

[Photo by Jean-Marc Giboux | RIBI Image Library | Flickr | cropped |Creative Commons 2.0]