Study provides crucial insights for targeting rapid response strategies and improving polio surveillance worldwide
A major new study in Nature Microbiology led by Imperial College London and supported by the Medicines and Healthcare products Regulatory Agency (MHRA) has uncovered critical insights into the spread patterns of vaccine-derived poliovirus type 2 (cVDPV2), offering valuable intelligence to support global efforts to eradicate polio.
The research, conducted by an international team including scientists from the MHRA's Vaccines, Science and Research Group, analysed 3,893 cVDPV2 cases across 74 outbreaks in 39 countries between May 2016 and September 2023.
Key findings
The study reveals that vaccine-derived poliovirus spreads at a consistent median velocity of 2.3 kilometres per day, predominantly between neighbouring countries. This represents the first comprehensive assessment of the spatiotemporal dynamics of cVDPV2 transmission since the global withdrawal of type 2 oral poliovirus vaccine in 2016.
Analysis shows that whilst most outbreaks remain relatively contained - with a median of just 4.5 cases - some have spread extensively, affecting up to 14 countries. International borders were found to significantly slow transmission, likely due to higher immunity levels created by vaccination campaigns, potentially decreasing spread velocity by up to 38%.
The research also demonstrates that historic wild-type poliovirus spread patterns closely resemble current cVDPV2 transmission routes, with movement largely sustained through unidirectional flow between adjacent countries.
Dr Javier Martin, the MHRA's Head of Polio Laboratory and a co-author of this paper, said:
"This study, which examines broad epidemiological patterns across multiple countries, provides crucial insights for targeting rapid response strategies and improving polio surveillance. Understanding historical spread patterns helps predict and prevent future outbreaks as global polio eradication efforts continue."
Implications for global health
These findings have significant implications for outbreak response strategies. By understanding the speed and patterns of virus spread, health authorities can better anticipate geographical reach when planning vaccination campaigns, potentially enabling more proactive preventive measures in neighbouring regions.
The study's lead researchers suggest that the current reactive approach - deploying vaccination campaigns following case detection - could be enhanced by considering preventive campaigns in neighbouring countries with low immunity levels.
Context
Vaccine-derived poliovirus emerges in rare instances when the weakened virus in oral polio vaccine mutates and regains the ability to cause paralysis. Whilst wild-type poliovirus has been largely eradicated globally, with type 1 now confined to just two countries (Pakistan and Afghanistan), cVDPV2 outbreaks have become a major challenge to complete polio eradication.
Since March 2021, a novel type-2 oral poliovirus vaccine (nOPV2), engineered to be more genetically stable. has been deployed under WHO Emergency Use Listing. The vaccine achieved full WHO prequalification in December 2023. The novel vaccine nOPV2 was designed in large part by scientists at the MHRA.
