Polio Eradication, 2018–March 2020: Wild Polio Rebounds as COVID-19 Halts Campaigns

Since the Global Polio Eradication Initiative (GPEI) began in 1988, two of the three wild poliovirus types have been eradicated — type 2 (certified in 2015) and type 3 (certified in October 2019, last seen in 2012). Wild poliovirus type 1 (WPV1) still spreads in only two countries, Afghanistan and Pakistan. This report covers January 2018 to March 2020.

Key findings

• In 2019, the two countries reported 176 WPV1 cases — the most since 2014.
• In January–March 2020, 54 cases were reported, about four times the 12 in the same months of 2019.
• Circulating vaccine-derived poliovirus (cVDPV) — which arises when the weakened virus in oral polio vaccine (OPV) circulates for a long time among underimmunized people and regains the ability to paralyze — spread too: 21 countries reported 547 type 2 cases.
• COVID-19 then suspended vaccination campaigns and disrupted surveillance.
• Nigeria has had no wild polio since September 2016, so the WHO African Region became eligible to be certified polio-free in 2020.

Wild polio

Wild poliovirus cases by country and month of onset, January 2017–March 2020. From CDC's MMWR.

• Pakistan: cases spread from 6 districts in 2018 to 43 in 2019, and early 2020 cases came from four provinces — Balochistan, Khyber Pakhtunkhwa, Punjab and Sindh. Sewage testing found WPV1 in 47% of samples in 2019 (up from 20%), at 56 of 60 sites. Virus of Pakistani origin also turned up in three sewage samples in Iran in early 2019.
• Afghanistan: cases came from 20 districts in 2019, up from 14; WPV1 was found in 22% of sewage samples.

Sewage samples had kept testing positive even during the 2014–2017 decline in cases, showing the virus never stopped circulating. Both countries face vaccine refusals, campaign fatigue and hard-to-reach mobile populations. In Afghanistan, antigovernment groups banned house-to-house vaccination in most southern and southeastern provinces from May to December 2018, allowed only site-based vaccination from January to April 2019, and then banned campaigns nationwide from late April to late September 2019. Pakistan's program went through a management review in 2019 to tackle longstanding community mistrust and vaccine hesitancy.

Vaccine-derived polio

Since type 2 OPV was withdrawn worldwide in April 2016, type 2 vaccine-derived outbreaks have grown in number and reach — mainly because outbreak-response campaigns with monovalent type 2 vaccine (mOPV2) were too slow, too small or of poor quality, and seeded new outbreaks elsewhere.

Most type 2 outbreaks were in Africa, but they also reached Afghanistan and Pakistan; one emergence from Nigeria spread to nine countries. In 2019, Angola reported 130 cases and the Democratic Republic of the Congo 88. A genetically stabilized novel OPV2 (nOPV2), much less likely to revert, was being prepared for use in late 2020 and will eventually replace mOPV2.

Vaccination and surveillance

• In 2018, 89% of infants worldwide got at least three polio vaccine doses and 72% at least one dose of inactivated polio vaccine (IPV); in Afghanistan the figures were 73% and 66%, in Pakistan 75% and 75%.
• Campaigns delivered about 1.2 billion bivalent OPV doses in 35 countries in 2018 and about 1 billion in 34 countries in 2019. Outbreak response used 100 million mOPV2 doses in 2018, 190 million in 2019 and 60 million so far in 2020.
• Polio is detected through acute flaccid paralysis (AFP) surveillance in children under 15, confirmed by stool testing, often backed by sewage testing. Of the countries with polio cases in 2018–2019, 11 met the main surveillance standards both years, while five — the Central African Republic, DRC, Malaysia, Papua New Guinea and the Philippines — met them in neither.

COVID-19

In March 2020, GPEI put its laboratories, surveillance network and thousands of trained polio workers at the service of the COVID-19 response. To keep physical distance, partners recommended postponing outbreak-response campaigns until at least June 2020 and preventive campaigns until the second half of 2020. Routine immunization and polio surveillance were disrupted, though new areas of spread were still being found.

What's needed

• Revitalize community engagement against campaign fatigue and hesitancy, strengthen basic health services and reach chronically missed children.
• In Afghanistan, negotiate to resume house-to-house campaigns.
• In Pakistan, carry out the 2019 review's recommendations and reach underserved minorities, including Pashtun communities.
• Use nOPV2 to prevent new type 2 emergences, and safely restart and scale up campaigns when COVID-19 allows.

Sources

Based on Chard AN, Datta SD, Tallis G, et al., "Progress Toward Polio Eradication — Worldwide, January 2018–March 2020," Morbidity and Mortality Weekly Report 69(25), CDC; a work of the United States government in the public domain.