Latest Efforts Moving Us Closer to Global Polio Eradication

Photo By: CDC Global (CC)

The world could soon witness what has been called one of the largest internationally coordinated public health efforts in history; the eradication of polio from the planet.

While polio has already been eliminated throughout much of the industrialized world, the disease still exists in some places causing permanent paralysis and even death for children younger than 5. There are three strains of wild polio virus (WPV) — types 1, 2, and 3. One in 200 infections leads to debilitating paralysis and 5% to 10% of people with these infections will die when their breathing muscles become immobilized. However, with nearly 3 billion children immunized over the past 20 years, incidence has decreased by 99% since 1988, according to the World Health Organization (WHO). Polio is currently endemic in Afghanistan and neighboring Pakistan, but public health experts and volunteers are making a last stand to eradicate the disease once and for all.

According to the Centers for Disease Control and Prevention, only 74 WPV cases were reported in two countries — Afghanistan and Pakistan — last year, a decrease of 79% from the 359 WPV cases reported in 2014 in nine countries. In the first two quarters of this year there were fewer cases than ever reported in history: Only 17 WPV cases compared with 29 during the same period in 2015.

Then, in April, an unprecedented campaign in the history of vaccines was achieved — the simultaneous switch to the bivalent oral polio vaccine (OPV) in 155 countries and territories. The most routine polio vaccination used around the globe up until this point was the trivalent OPV, which contained three types of live, attenuated vaccine-viruses. After immunization, the vaccine replicates in the intestine and then excreted. In areas where sanitation and hygiene are lacking, immunization with OPV can result in the “passive” immunization of people who have not been directly vaccinated while also boosting the immune response for those who have.

However, approximately 1 out of every 2.7 million doses of the OPV vaccine can cause paralysis. In areas with enough susceptible children and low vaccination coverage, the excreted viruses can genetically mutate and begin circulating, causing paralytic cases in populations with low immunity; this is known as circulating vaccine-derived polioviruses (cVDPV). Most of the cVDPV cases prior to 2015 were type 2. Since there has not been a case of WPV2 since 1999, WHO’s Strategic Advisory Group of Experts on Immunization (SAGE) recommended the synchronized switch from the trivalent OPV to the bivalent OPV in April. The newest vaccine provides protection against WPV type 1 and type 3 while reducing risk of vaccine-associated paralytic poliomyelitis (VAPP) and type 2 vaccine-derived polioviruses (cVDPV2s). Bolstered by progress made during 2015-2016 on interrupting WPV transmission in Afghanistan and Pakistan, this is part of the polio endgame strategic plan. If dedicated vaccination efforts remain throughout the next year, polio will soon join smallpox and rinderpest to become only the third infectious disease to be successfully eradicated from the planet. A spectacular achievement in the history of science and medicine.