Most (86%) of these outbreaks were caused by cVDPV2 (circulating VDPV type 2 poliovirus, which originated with the vaccine), and most occurred in Africa, according to a new study of vaccine-derived poliovirus outbreaks between Jan. 2020 and June 2021 published in the CDC’s Morbidity and Mortality Weekly Report.
The Global Polio Eradication Initiative (GPEI) was launched in 1988 and used live attenuated oral poliovirus vaccine (OPV). Since then, cases of wild poliovirus have declined more than 99.99%.
The cVDPV2 likely originated among children born in areas with poor vaccine coverage. Jay Wenger, MD, director, Polio, at the Bill and Melinda Gates Foundation, told this news organization that “the inactivated vaccines that we give in most developed countries now are good in that they provide humoral immunity, the antibodies in the bloodstream. They don’t necessarily provide mucosal immunity. They don’t make the kid’s gut immune to getting reinfected or actually immune to reproducing the virus if they get it in their gut. So we could still have a situation where everybody was vaccinated with IPV [inactivated poliovirus], but the virus could still be transmitting around because kids’ guts would still be producing the virus and there will still be transmission in your population, probably without much or any paralysis because of the IPV. As soon as that virus hit a population that was not vaccinated, they would get paralyzed.”
Dr. Wenger added, “The ideal vaccine would be an oral vaccine that didn’t mutate back and couldn’t cause these VDPVs.” Scientists developed such a vaccine, approved by the World Health Organization last year under an Emergency Use Authorization. This nOPV2 (novel oral poliovirus type 2) vaccine has been given since March 2021 in areas with the VDPD2 outbreaks. The nOPV2 should allow them to “basically stamp out the outbreaks.”
The world had almost eradicated the disease, with the last cases of polio from wild virus occurring in Nigeria, Afghanistan, and Pakistan as of 2014. Africa was declared free of wild polio in 2020 after it had been eradicated from Nigeria, which accounted for more than half of the world’s cases only a decade earlier. Now cVDPV outbreaks affect 28 African countries, plus Iran, Yemen, Afghanistan, Pakistan, Tajikistan, Malaysia, the Philippines, and Indonesia. And there was also one case in China. Globally, there were 1,335 cases of cVDPV causing paralysis during the reporting period.
The COVID-19 pandemic has had a significant impact on polio, accounting for much of this year’s increase in cases. Dr. Wenger said, “We couldn’t do any campaigns. We pretty much stopped doing outbreak response campaigns in the middle of the year because of COVID.”
The CDC report notes that many of the supplementary immunizations in response to cVDPV2 outbreaks were of “poor quality,” and prolonged delays enabled geographically expanding cVDPV2 transmission.
Steve Wassilak, MD, chief coauthor of the CDC study, told this news organization that, because of COVID, “what we’ve been lacking is a rapid response for the most part. Some of that is due to laboratory delays and shipment because of COVID’s effect on international travel.” He noted, however, that there has been good recovery in surveillance and immunization activities despite COVID. And, he added, eradication “can be done, and many outbreaks have closed even during the [COVID] outbreak.”
Dr. Wassilak said that in Nigeria, “the face of the campaign became national.” In Pakistan, much of the work is done by national and international partners.
Dr. Wenger said that in Nigeria and other challenging areas, “the approach was essentially to make direct contact with the traditional leaders and the religious leaders and the local actors in each of these populations. So, it’s really getting down to the grassroots level.” Infectious disease officials send teams to speak with individuals in the “local, traditional leader system.”
“Just talking to them actually got us a long way and giving them the information that they need. In most cases, I mean, people want to do things to help their kids,” said Dr. Wenger.
For now, the initial plan, per the CDC, is to “initiate prompt and high coverage outbreak responses with available type 2 OPV to interrupt transmission” until a better supply of nOPV2 is available, then switch to IPVs.
Dr. Wenger and Dr. Wassilak report no relevant financial relationships.
A version of this article first appeared on Medscape.com.