CDC's Polio Surge Against Vaccine-Derived Poliovirus Outbreaks, 2019–2020

In April 2016, following a resolution of the 68th World Health Assembly and in coordination with the Global Polio Eradication Initiative (GPEI), the type 2 component of the Sabin-strain oral poliovirus vaccine (OPV) was withdrawn from all immunizations worldwide, to prevent outbreaks of type 2 circulating vaccine-derived poliovirus (cVDPV2).

Growing outbreaks

Before the switch, in early 2016, 42 at-risk countries with weak routine immunization ran house-to-house campaigns with trivalent OPV to close type 2 immunity gaps. But some campaigns were poor, leaving pockets of unvaccinated and under-vaccinated children. Monovalent type 2 OPV (mOPV2) then successfully stopped many cVDPV2 outbreaks — but some in sub-Saharan Africa weren't quickly controlled and spread to other countries, and where mOPV2 campaigns were of low quality, prolonged circulation of the vaccine strain let new outbreaks emerge.

• In 2019, 358 cVDPV2 cases were reported, up from 71 in 2018, and the number of countries with outbreaks more than tripled, from five to 16.
• As of August 2, 2020, 236 cases had been reported in 17 countries that year.
• Of 33 cVDPV outbreaks reported between July 2018 and February 2020, 31 (94%) were type 2.

The surge

CDC's Emergency Operations Center, running a polio response since December 2011, launched a "polio surge" in September 2019 to support country programs alongside its ongoing technical help.

• CDC recruited volunteers with international experience and outbreak skills and gave them a three-day training on surveillance, eradication strategies, campaign planning and implementation, supportive supervision and country briefings.
• Countries were chosen for active outbreaks or high risk, field access, and the presence of other key staff, such as CDC-supported Field Epidemiology Training Program residents and Stop Transmission of Polio consultants.
• Surge staff worked in frontline field positions, strengthening coordination, planning and supervision to improve vaccination campaigns and surveillance. Most went to outbreak countries in sub-Saharan Africa and the Philippines; five supported preparedness in high-risk neighbors, such as Namibia, which shares a porous border with Angola.
• In all, 108 surge staff deployed to 13 countries over six months, 12 of them with CDC offices or staff. Some outbreak countries couldn't be reached because of safety and access concerns.

CDC polio surge deployments, September 2019–March 2020 (MMWR).

COVID-19 intervenes

As the COVID-19 pandemic restricted international travel, CDC first pulled deployed staff back to its country offices in capital cities, then — by March 23, 2020 — brought home all 32 surge staff deployed that month. On March 26, the GPEI recommended postponing OPV campaigns until at least June 2020. CDC began contracting experienced local Field Epidemiology Training Program and Stop Transmission of Polio alumni to keep the response going, while GPEI field staff shifted much of their time to COVID-19 surveillance and control.

Disrupted routine immunization and campaigns raised the risk of vaccine-preventable diseases, including polio, as continued cVDPV2 spread showed. Response mOPV2 campaigns resumed in late July, and surge deployments can resume once mission-critical international travel is allowed.

Despite the cVDPV2 challenge, progress against wild poliovirus continued: on August 25, 2020, the World Health Organization's African Region was certified free of indigenous wild poliovirus transmission, joining the Americas, European, South-East Asia and Western Pacific regions.

Sources

• Meyer E, Sikka N, Durry E, Datta D. "Notes from the Field: CDC Polio Surge Response to Expanding Outbreaks of Type 2 Circulating Vaccine-Derived Poliovirus — Africa and Philippines, September 2019–March 2020," MMWR Vol. 69, No. 34, CDC; a work of the United States government in the public domain.