Polio used to be one of the most feared diseases around the world. Only a few decades ago, it was a very common paralyzing disease that mainly affected children under 5 years old. However, due to the hard work of health organizations like WHO and UNICEF, along with the cooperation of governments worldwide, we have come a long way in eradicating this crippling disease through mass immunization efforts using IPV vaccines. In this article, we will discuss the role of IPV vaccines in eliminating polio, current vaccination strategies and challenges that remain.
History of Polio Vaccines
In the early 20th century, before vaccines were developed, polio outbreaks occurred annually during summer months in temperate climates. Thousands of children were paralyzed or even died as a result of polio infections each year. It was only in the 1950s that breakthroughs occurred, with two safe and effective polio vaccines: the Salk inactivated poliovirus vaccine (IPV) in 1955 and the Sabin live attenuated oral poliovirus vaccine (OPV) in 1960. While both vaccines provided protection, IPV required multiple injections and was more expensive. OPV, which contains weakened live viruses, could be given as oral drops and was effective at stopping polio outbreaks. By the late 1980s, OPV was used almost exclusively worldwide during the global polio eradication initiative.
Moving to IPV-Only Strategy
While OPV was highly effective in bringing polio cases down globally, it carries a rare risk of vaccine-derived polio cases. In very rare instances, the live attenuated virus in OPV can mutate back into a form that can cause disease. To close this very small risk and complete polio eradication, in a unanimous decision in May 2016, the World Health Assembly resolved to switch all OPV-using countries to exclusive IPV use in their routine immunization programs between 2016 and 2019. This transition involved around 100 countries worldwide switching from trivalent OPV to IPV in their routine programs along with continuing supplementary OPV doses. The globally synchronized switch is a remarkable public health achievement executed precisely as planned without any glitches. Today only IPV is used around the world for routine immunization against polio, eliminating any risk of vaccine-derived polio outbreaks.
IPV Effectiveness and Schedule
IPV Vaccines contains inactivated polioviruses that cannot cause polio but can still provoke an immune response and provide protection. It is given through intramuscular injection, usually in the thigh for infants. The global IPV schedule today as recommended by WHO is a four-dose schedule given at 6, 10 and 14 weeks of age followed by a booster between 15-18 months. Studies have found this regimen is around 90% effective in preventing paralytic polio and provides immunity that lasts for many years. However, IPV alone cannot interrupt polio transmission. It is used today alongside continuing outbreak response using monovalent OPV2 in low transmission regions to fully eradicate any remaining polioviruses. The IPV doses train the immune system to recognize and respond to polioviruses, priming it for any OPV doses.
Challenges With IPV
While IPV provides highly effective individual immunity, its use alone is unable to generate widespread population immunity levels required to stop poliovirus transmission. As IPV is injected, it is more expensive than the oral OPV drops and requires trained healthcare staff. Ensuring high IPV coverage remains an ongoing challenge, especially in remote communities and conflict-affected areas where OPV campaigns tend to reach more children. Additionally, global IPV supply is relatively limited compared to the vast doses needed for supplementary immunization activities. There is currently only one prequalified global supplier providing almost all the world’s IPV needs. Efforts are underway to expand the production capacity and supplier base to meet the anticipated future demand. Despite these challenges, IPV provides a safe vaccination option for countries to rely on exclusively in their routine programs for achieving a polio-free world.
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