Scientists at the Medicines and Healthcare products Regulatory Agency (MHRA) have jointly led an international study published today in Nature Microbiology examining the genetic stability of the novel live-attenuated oral poliovirus type 2 vaccine (nOPV2) used in global polio eradication efforts.
The research – conducted in partnership with institutions across Uganda, the United Kingdom, Israel, France, the Netherlands, the United States, and the World Health Organization – provides important insights into how the vaccine evolves following administration and demonstrates its enhanced stability compared to previous oral polio vaccines. The novel vaccine nOPV2 was designed in large part by scientists at the MHRA.
Key findings
The study analysed 231 poliovirus type 2 isolates collected from stool and sewage samples in Uganda between January 2022 and March 2023, following nOPV2 vaccination campaigns. Researchers found that nOPV2 demonstrates higher genetic stability than the previously used Sabin oral polio vaccine, with genetic modifications in the vaccine – particularly the stabilization of the main genetic domain responsible for attenuation.
However, the study also identified a rare double recombinant strain that emerged through genetic recombination with other enteroviruses circulating in the population. Whilst this strain showed increased neurovirulence in laboratory testing, it did not spread widely, likely due to high vaccination coverage in the affected area.
Dr Javier Martin, The MHRA’s Head of Polio Laboratory and co-author of this paper, said
This study confirms nOPV2 is performing as designed to interrupt polio outbreaks whilst reducing the risk of new vaccine-derived outbreaks. Uganda successfully interrupted circulating vaccine-derived poliovirus transmission following two nationwide nOPV2 campaigns reaching approximately 20 million children.
MHRA’s contribution
MHRA’s WHO Global Specialised Laboratory for Polio conducted extensive whole-genome sequencing analysis of virus samples using advanced Illumina and Oxford Nanopore sequencing technologies. The agency’s scientists analysed viral genetic material spotted on FTA cards and conducted additional characterisation of sewage samples to confirm findings.
Work at MHRA was supported by funds from the National Institute for Health Research (NIHR) Policy Research Programme (Regulatory Science Research Unit), MHRA core funding, and a grant from the Bill and Melinda Gates Foundation.
Implications for global polio eradication
The findings underscore the reduced risk of reversion to dangerous forms with nOPV2 compared to previous oral polio vaccines, whilst highlighting the continued importance of robust surveillance systems to detect and respond to rare genetic changes.
The research supports the continued use of nOPV2 alongside inactivated polio vaccine, combined with strong immunisation programmes and vigilant monitoring, as part of global efforts to achieve and sustain polio eradication.
Notes to editors
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The Medicines and Healthcare products Regulatory Agency (MHRA) is responsible for regulating all medicines and medical devices in the UK by ensuring they work and are acceptably safe. All our work is underpinned by robust and fact-based judgements to ensure that the benefits justify any risks.
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The MHRA is an executive agency of the Department of Health and Social Care.
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The DOI number for this paper is 10.1038/s41564-025-02219-w and it is available at the following URL https//www.nature.com/articles/s41564-025-02219-w
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The study was conducted through collaborative partnership involving the Uganda Virus Research Institute, MHRA, Tel Aviv University, Institut Pasteur Paris, the National Institute for Public Health and the Environment (RIVM) in the Netherlands, the Bill & Melinda Gates Foundation, and the World Health Organization Regional Office for Africa.
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All genomic sequences generated in this study have been deposited in publicly accessible databases.
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Animal studies to assess the neurovirulence of isolated strains were performed at MHRA under strict ethical approval, adhering to UK regulations governing animal research and welfare standards.
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The World Health Organization continues to classify poliovirus spread as a Public Health Emergency of International Concern.
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The views expressed in the publication are those of the authors and not necessarily those of the funders, NHS, NIHR, Department of Health, arm’s length bodies, or other government departments.
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