Medical Science

Live-attenuated viruses used in oral polio vaccines can cause infections

by Mahfuzul Hasan

Infection with polioviruses causes paralysis in severe cases as the virus can cause paralysis in the spinal cord, brainstem or both. Although only 1 percent can experience such severe consequences while the majority remain asymptomatic. Infection with polio virus can stimulate lifelong immunity against the virus and based on these characteristics, different types of polio vaccines were developed and distributed. There are three different serotypes of polio viruses and infection with one particular type does not develop immunity against other two. This made the vaccine development process more complex and discovery of effective vaccines for tackling paralytic polio can be considered as a tremendous medical breakthrough of the past century. In fact, two different types of vaccines gained popularity and used all over the world (Poliomyelitis, n.d.):

  1. Inactivated polio vaccine (IPV): This vaccine was first developed by Dr. Jonas Salk which contained wild type poliovirus strains of each three serotypes that have been inactivated (killed) using formalin. Generally, three doses were administered through injection which was later followed by a booster dose. 
  2. Oral polio vaccine (OPV): This vaccine was developed by Dr. Albert Sabin and contained a live-attenuated mixture of the poliovirus strains. These weakened viruses had the ability to mimic the immune response similar to the wild type viruses. However, the viruses were weakened in such a way that they cannot reach the nervous system and lack the ability to cause paralysis. 

Among these two types, the oral vaccines became more popular due to the following advantages:  

  • Oral vaccines were proven to induce much significant mucosal immunity compared to IPV. In fact, the site of the multiplication of the virus in humans is the intestines and the induction of local immune responses at the intestine prevented the multiplication of the virus. Therefore, mass campaign with OPV prevented person to person transmission of the virus (Poliomyelitis, n.d.). 
  • Storage and transportation of oral vaccines did not require refrigeration which provided advantages for countries with lower and lower-middle economies. 
  • Overall operation cost is less with oral vaccines as injection, syringe and personnel capable of injecting are not required. 

Due to all these reasons, the oral vaccines were adopted and are still being used all around the globe. However, the attenuated viruses used in oral vaccines are capable of mutation. Few types of research showed that, these viruses can evolve into more virulent forms than their wild type precursors and even have the probability of causing outbreaks (Michigan Medicine – University of Michigan, 2020). In the past year, the effects of such vaccine-derived mutated viruses have been evident in countries such as The Republic of Congo, Central African Republic and Angola. In fact, if we observe the statistics, the total number of such infection from vaccine derived polio was 157 in 2019 whereas the number of wild type cases was 107(Akst, 2019). So, this data shows that the number of infections due to vaccine derived polio is higher than the wild-type infection. Many researches are required to predict the actual condition regarding this issue. In fact, one such research was performed by researchers of Mami Taniuchi, Ph.D., of the University of Virginia and Michael Famulare, Ph.D. of the Institute for Disease Modeling in Seattle, Washington and team of scientists from the International Center for Diarrhoeal Disease Research, Bangladesh. They collected stool samples from households of children who were vaccinated and viruses from these samples were genetically analyzed. Their research found three mutations that caused the virus to become virulent again (Michigan Medicine – University of Michigan, 2020). We can be optimistic about the fact that, subsequent researches in this field would be able to identify and prevent future outbreaks.

Mahfuzul Hasan

Microbiology Program, Department of Mathematics and Natural Sciences,

BRAC University


  1. Poliomyelitis. (n.d.). World Health Organization. Retrieved December 18, 2020, from,-OPV%20consists%20of&text=OPV%20produces%20antibodies%20in%20the,poliovirus%20to%20the%20nervous%20system
  2. Michigan Medicine – University of Michigan. (2020, November 18). How the polio vaccine virus occasionally becomes dangerous: Genetic study of the live vaccine could help efforts toward eradication. ScienceDaily.
  3. Akst, J. (2019, November 25). Polio Vaccination Causes More Infections than Wild Virus. The Scientist Magazine®.

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