More than 150 countries have launched a vaccine switch on April 17 in a final attempt to eradicate polio once and for all within the next two years. The switch from trivalent oral poliovirus vaccine (tOPV) to bivalent oral poliovirus vaccine (bOPV) would protect one against types 1 and 3 polio virus, the two remaining polio strains.

The trivalent oral poliovirus vaccine has eliminated Type 2 wild polio after causing more than 90 percent of polio cases in the last 10 years. However, the old vaccine can mutate and result to vaccine-derived polio, also known as circulating vaccine-derived polioviruses (cVDPV).

The global vaccine switch to bivalent oral poliovirus vaccine (bOPV) would eliminate these risks associated with the type 2 vaccine strain. Moreover, this would also increase the protection against the last polio strains.

eradicate polio

A child is vaccinated with an oral poliovirus vaccine. WHO/Afghanistan

“We’re closer than ever to ending polio worldwide, which is why we are able to move forward with the largest and fastest globally synchronised vaccine switch ever,” asserts Michel Zaffran, the director of Polio Eradication at the World Health Organisation (WHO). “It is a massive undertaking, but it is testimony to how much progress is being made toward achieving a lasting polio-free world and to the commitment of all countries to make this dream a reality.”

Health experts call this the largest and fastest globally coordinated launch of a new vaccine into routine immunisation programme the world has ever since. They insist that the switch must be globally synchronised because a type 2 poliovirus would affect those who stopped using tOPV if some nations continue to use this old vaccine.

Reza Hossaini, chief of Polio at UNICEF, says that hundreds of thousands of health workers and vaccinators have been trained to ensure the smooth and effective transmission. Thousands of independent monitors have also been tasked to confirm the absence of tOPV in all health service facilities, both public and private, to see that the switch goes as planned.

Apart from bOPV, a dose of inactivated polio vaccine (IPV) is added to routine immunisation programmes in countries at higher risk of a polio outbreak. A global stockpile of monovalent OPV (mOPV) type 2 is also available in case of a post-switch outbreak of cVDPV type 2.

The global vaccine switch milestone exemplifies moving toward the right direction toward global eradication. While fewer cases have been reported in fewer countries than before in 2015, Michael McGovern, chair of Rotary’s International PolioPlus Committee, says that global support is still of utmost importance to eradicate the disease once and for all.