Update on Vaccine-Derived Poliovirus Outbreaks Worldwide.
A Post-Polio Article Review
The Morbidity and Mortality Weekly Report (MMWR) is prepared by the Centers for Disease Control and Prevention (CDC) to report on causes of death and illness in the U.S. and around the world. The MMW reports are comprehensive, data packed. . . and long, not to be read in bed unless you need to treat insomnia. But these detailed reports are vital if you want to know about the cause and treatment of just about any disease, including polio.
Since polio survivors are interested in eradication efforts around the world, this article in our series “POST-POLIO ARTICLE REVIEW” summarizes the June 19, 2023 MMWR describing the hiccups causing vaccine-derived poliovirus outbreaks worldwide . . .
Update on Vaccine-Derived Poliovirus Outbreaks Worldwide: January 2021-December 2022
Morbidity & Mortality Weekly Report. 2023;72(14): 366-371.
With the September, 2015 elimination of wild (naturally occurring) type 2 poliovirus, the use of the Sabin-strain oral poliovirus vaccine type 2 (OPV2) was stopped in April, 2016. Countries switched from the trivalent vaccine (containing poliovirus types 1, 2 and 3) to the bivalent form of OPV, which contains only poliovirus vaccine types 1 and 3.
But the removal of a vaccine for type 2 poliovirus left people susceptible to the still-circulating type 2 oral polio vaccine strain and its unfortunate ability to circulate and, without causing symptoms, reproduce in the intestines of 90% of those infected. In the intestines, the vaccine poliovirus can genetically mutate, become neurovirulent (damaging to neurons) and itself cause paralysis. There were 959 OPV2–polio cases globally in 2020 alone, most in Africa.
In 2021, a novel Oral Polio Vaccine type 2 (nOPV2) - a more genetically stable vaccine than Sabin OPV2 that was much less likely to mutate and cause paralysis, was released. Unfortunately, the extensive use of nOPV2 during 2021-2022 resulted in a lack of adequate nOPV2 supply that has often been insufficient for prompt response to polio outbreaks.
Vaccine-Derived Polio Virus Data
During 2021–2022, there were 88 active, community circulating Vaccine-Derived Polio Virus (cVDPV outbreaks), 76 (86%) caused by cVDPV2.
The total number of paralytic cVDPV cases during 2020–2022 decreased by 36%, from 1,117 to 715; however, the proportion of cases caused by cVDPV type 1 increased from 3% in 2020 to 18% in 2022, The increased proportion of cVDPV1 cases follows a substantial decrease in global routine immunization due to preventive COVID immunization campaigns during the pandemic (2020–2022).
cVDPV2 (Circulating Vaccine Derived Poliovirus Type 2)
The decrease in the number of new cVDPV2 cases during this period is likely associated with the use of nOPV2 for outbreak response. Since the first cVDPV2 outbreak response using nOPV2, as of March 2023 590 million nOPV2 doses have been administered in 24 countries. Whereas the number of cVDPV2 appearances has declined during the 2021–2022 COVID pandemic and recovery period, international spread has not. During the last 2 years, 17 countries have experienced their first post-nOPV2 vaccine use cVDPV2 outbreaks, reflecting poor outbreak control in the country of origin.
cVDPV1 (Circulating Vaccine Derived Poliovirus Type 1)
In 2022, the number of new cVDPV1 outbreaks increased substantially and primarily affected countries in sub-Saharan Africa. Routine immunization coverage, which was already low in many areas of outbreak countries, decreased after the start of the COVID-19 pandemic. Plus, the suspension of preventive and supplementary bOPV (Bivalent Oral Polio Vaccine type I and type III) vaccination have resulted in an increased susceptibility to cVDPV1 outbreaks.
During 2022, the national proportion of African children who received their third dose of polio vaccine by age 1 year was 70%, compared with 74% in 2019.
Conclusion
Increasing routine immunization coverage, strengthening poliovirus surveillance and conducting timely and high-quality supplementary immunization in response to cVDPV outbreaks are all needed to interrupt global cVDPV transmission and reach the goal of no cVDPV in 2024.