Brazil, Other Countries at Risk for Reintroduction of Polio

Mônica Tarantino

November 03, 2021

Brazil is one of six countries in the Americas at high risk for the reintroduction of polio, according to the Pan American Health Organization (PAHO). The others are the Dominican Republic, Ecuador, Guatemala, Suriname, and Venezuela. Another two countries, Haiti and Bolivia, are at very high risk, PAHO member Luiza Helena Falleiros, MD, PHD, pediatrician and infectious disease specialist at the Metropolitan University of Santos in Brazil, said during the October 19 webinar, entitled Why Do We Still Need to Talk About Polio? The event was sponsored by Sanofi Pasteur, which manufactures inactivated vaccines.

Since 2015, Brazil has faced a troubling decline in vaccination rates for polio and other contagious diseases.

"Currently, among children up to 1 year of age, we have just 62% polio vaccination coverage with the primary immunization series, which consists of three doses of inactivated polio vaccine (IPV). So roughly 40% of children did not receive the primary series that they should have," said Falleiros.

The goal is to have at least 95% of the eligible population vaccinated against polio, she said. "There is a concern about what the future holds. We have to think about which integrated solutions will get us back to where we were coming into the 21st century."

The immunization dropout rates are another cause for concern. "The number of children receiving polio vaccine boosters at 15 months and at age 4 is even lower," said Juarez Cunha, MD, pediatrician and president of the Brazilian Immunization Society. Of the 2.7 million children born in 2020, 2.4 million received the first dose of the vaccine and 2.2 million received the third dose. "If we think about these numbers, we're talking about 500,000 children who are not adequately vaccinated and protected," he said.

In Brazil, the national child immunization schedule recommends a polio vaccination series that consists of IPV administered at 2, 4, and 6 months plus the oral polio vaccine (OPV) booster administered at 15 months and at 4 years.

The switch from the trivalent oral vaccine (against the three poliovirus serotypes) to the bivalent OPV was recommended by the World Health Organization (WHO) in 2018. The WHO's current guidance advises that countries gradually replace OPV with IPV. "The inactivated vaccine is the only one that is going to provide protection against the three serotypes of the virus. Several Latin American countries already use just the inactivated vaccine. In Europe, the oral vaccine hasn't been used for many years," said Falleiros. The switch is warranted, she explained, to prevent an uncommon adverse event in which the live attenuated virus mutates in a human host and becomes active again. Although this is very rare, specialists fear that as vaccination coverage falls, reactivation will increase, and vulnerable children will be more likely to come into contact with the virus.

Global Cases of Wild Poliovirus

In January, there were two recorded cases of wild poliovirus in the world: one in Pakistan and the other in Afghanistan. "In 2020, there were 63 cases," said Cunha. Five of six WHO regions are now certified as being free of the wild poliovirus, according to the Global Update issued by the Global Polio Eradication Initiative. Brazil saw its last case in 1989, and the Americas received certification of polio eradication in 1994.

However, a new challenge emerged in 2019, according to the update: a growing public health emergency due to circulating vaccine-derived poliovirus type 2 (cVDPV2). In August 2020, 323 cases of cVDPV2 and 84 environmental samples positive for cVDPV2 were reported by 20 countries, most of them in Africa, but including Afghanistan, Pakistan, and the Philippines.

As soon as poliovirus — whether wild or vaccine-reactivated — starts to circulate, the low vaccination coverage could bring about the reintroduction of the disease. "It took us almost 50 years to eliminate measles. Due to low vaccination coverage, it came back in two. There hasn't been a case of polio in Brazil for 30 years. It is hard to imagine that this disease could come back because of low vaccination coverage. We have to vaccinate our population, not only against polio, but against all diseases for which vaccines are available," said Cunha.

This article originally appeared in the Portuguese edition of Medscape.

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