Trending Clinical Topic: Polio

Ryan Syrek


March 04, 2022

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Key findings and information related to vaccination, as well as news of an outbreak, made polio this week's top trending clinical topic. Health authorities in Malawi have declared an outbreak of wild poliovirus type 1 (see Infographic).

The Global Polio Eradication Initiative (GPEI) said in a statement that sequencing of the virus was conducted this month by the National Institute for Communicable Diseases in South Africa, and the Centers for Disease Control and Prevention confirmed the case as wild poliovirus type 1. According to the World Health Organization announcement, laboratory analysis shows that the strain identified in Malawi is linked to one that is circulating in Sindh Province in Pakistan. Polio remains endemic only in Afghanistan and Pakistan. Whether the 3-year-old girl had traveled to Pakistan is unknown. Kacey C. Ernst, PhD, MPH, a professor and infectious disease epidemiologist at the University of Arizona's Zuckerman College of Public Health in Tucson, said that although this is a cause for concern, it is "not a reason to panic. Malawi has very high polio vaccination rates and it is quite possible that this will be a very small defined outbreak that will be well-contained."

Africa was certified as wild poliovirus-free in August 2020. Africa will retain that status, the WHO states, because the strain originated in Pakistan. According to the WHO, only five cases of wild poliovirus were identified globally in 2021. The GPEI is sending a team to Malawi to support emergency operations, communications, and surveillance. Partner organizations are also sending teams. The GPEI partnership has included the Bill & Melinda Gates Foundation. Earlier in February, Bill Gates visited Pakistan and suggested that polio eradication may be possible in the coming years. However, he suggested that the outcome is uncertain, particularly given the situation in Afghanistan, where the Taliban took control in August. "Afghanistan is a little bit of a question mark because that's a more complex situation," he said, but noted vaccination rates had gone up this year after dropping off since 2018.

Beyond Africa, Pakistan, and Afghanistan, the Pan American Health Organization (PAHO) declared late last year that Brazil is one of six countries in the Americas that are at high risk for the reintroduction of polio. The others are the Dominican Republic, Ecuador, Guatemala, Suriname, and Venezuela. Another two countries, Haiti and Bolivia, are also at very high risk. Since 2015, Brazil has faced a troubling decline in vaccination rates for polio and other contagious diseases. Luiza Helena Falleiros-Arlant, MD, PhD, pediatrician and infectious disease specialist at the Metropolitan University of Santos in Brazil, explained that "[c]urrently, 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." The goal is to have at least 95% of the eligible population vaccinated against polio, she said.

Vaccination against polio may come with an added benefit. A recent study in Iran found that mothers of children immunized with the oral polio vaccine (OPV) appeared to have been protected against symptomatic COVID for at least 6 months. As reported in JAMA Network Open, from a cohort of close to 88,000 women, researchers analyzed data from 419 mothers (mean age, 35.5 years) who were indirectly exposed to OPV and 3771 age-matched women with no exposure to OPV from March to December 2020. None of the mothers whose children had received OPV developed COVID after a median follow-up of 141 days; 28 women (0.74%) in the unexposed group were diagnosed with COVID. Indirect exposure to OPV was found to be significantly associated with decreased COVID. At 9 months, the probability of remaining uninfected with COVID was 1.000 in the exposed group compared with 0.993 in the unexposed group.

From an ongoing outbreak to vaccine-related news, polio has been of notable global interest recently, resulting in this week's top trending clinical topic.

Learn more about polio.


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