By the 20th century, few diseases frightened parents more than the fever, chills, and paralysis delivered by the poliovirus. In response to the epidemic, we saw the development and distribution of two polio vaccines that drastically helped eradicate the virus. Unfortunately, this improved technology has its consequences. As vigorous vaccination programs target the last few countries still suffering from endemic polio, polio is now also the first virus to be recreated in the lab. After all our efforts to eradicate this virus, the question arises: when do you stop vaccinating?

Polio—a gastrointestinal virus—infects and multiplies within the digestive tract. Depending on the virus, it may leave the digestive tract and move into the bloodstream from where it can attack nerve cells. Although only one to two per cent of patients who contract polio become paralyzed, the polio epidemic of the 20th century caused a widespread fear in North America.

While polio has plagued humanity in the past—archeologists found an Egyptian carving from around 1400 that depicts a man with a leg deformity similar to those caused by polio—the virus reached epidemic proportions at the start of the 20th century. Ironically, this occurred while the prevalence of other viruses, such as diphtheria and typhoid, decreased.

“That is sort of the contradiction for polio,” said Jose Teodoro, assistant professor and researcher at the Rosalind and Morris Goodman Cancer Centre in Montreal. “It is one of these diseases that emerged in the 20th century when hygiene and sanitation got better.”

Teodoro explained that this phenomenon was largely due to the fact that polio is spread through the fecal-oral route.

“Before [the 20th century], children were exposed to polio [earlier] because there were no sanitation systems, so people used rivers or [other places] and that is where they got rid of fecal matter [….] When children at a very young age were exposed to [polio] they were already protected by [their mother’s antibodies if breastfed] and were able to develop a good immunity to it when they were young,” Teodoro said.

“We fast-forward to the 20th century and modern sewage systems that disrupt the fecal-oral route, and children become exposed to it much later—after they already lost their mother’s antibodies,” he added.

In response to this epidemic, Western countries saw two major breakthroughs with regards to eradicating the poliovirus. Within 10 years, two vaccines were developed— the Salk vaccine that consists of an inactivated poliovirus, released in 1955, and the Sabin vaccine, also known as the oral polio vaccine (OPV), licensed in 1962.

“[The Salk vaccine] worked, and for all of its flaws—it was not the perfect vaccine—it started to reduce the cases of polio immediately,” Teodoro said. “The Sabin vaccine that came later was the live attenuated vaccine. It is dropped into the mouth and goes into the gut to confer a powerful immune response to the replicating virus causing the disease.”

According to Teodoro, although both vaccines were huge steps in the direction of eradicating poliovirus, the Sabin vaccine (OPV) had the biggest impact on the eradication of the virus. For the first time in the history of polio vaccination, developing countries were able to acquire and distribute the vaccine due to its more accessible cost.

These technological developments were huge breakthroughs with regards to eradicating the poliovirus. Still, Teodoro explains that the biggest barrier right now is geopolitics. Countries such as war-torn Syria and Afghanistan are difficult to reach, and as a result, these countries are the last ones where endemic polio is still rampant. Many of the vaccination programs are spearheaded by Western organizations; however, these countries facing endemic polio are often too dangerous for workers to effectively run their programs.

Teodoro notes that the cost of the vaccine will become a problem in the future.

“Cost will become an issue because OPV is the method used to vaccinate people—it is the cheapest way—but to truly eradicate polio you have to go to the injectable polio vaccine (IPV), which is much more expensive.” Teodoro said.

An even bigger question faced today is the role that improved technology will have on the vaccination programs of viruses like polio. Recently, scientists recreated the poliovirus in the lab by plugging in the nucleotide sequence (the genetic code) of the poliovirus into an oligonucleotide-synthesizing machine. Using the nucleotide sequence, the machine generated a fully functional infectious polio agent.

“With polio—and almost any virus that you start eradicating—it is so easy to bring [it] back,” Teodoro said. “Any malicious group could synthesize it and make a real virus and introduce it into the population—a population that has not been vaccinated anymore. Even though we have eliminated the virus, do we now render the population defenseless against it?”

Teodoro proposes that the simplest answer to this question is to keep vaccinating. However, he also acknowledges that as we begin to eradicate more and more diseases, we may come to a point where we say “enough is enough.”

“Technology is a double-edged sword,” Teodoro said. “You can do great good with it but also you can do great harm if that is what your intention is to do. It enables both […]; should we be getting a vaccine for a potentially eradicated virus? It may be something that we have to keep doing, [or we may reach a point where] we just hope for the best. If something comes up, you deal with it—but we hope it never comes to that.”