A new study has confirmed the novel vaccine being used in global efforts to achieve and sustain polio eradication is successfully interrupting polio outbreaks whilst minimising risk of new vaccine-derived outbreaks in Uganda.
Scientists at the Medicines and Healthcare products Regulatory Agency (MHRA) have jointly led an international study, published 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 (WHO) – 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.
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 stabilisation 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 the 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 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.
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.
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 WHO Regional Office for Africa.
- Tushabe P, Majumdar M, Carlyle S, et al. Higher stability of novel live-attenuated oral poliovirus type 2 (nOPV2) despite the emergence of a neurovirulent double recombinant strain in Uganda. Nat Microbiol (2026). Published online 19 January. doi:10.1038/s41564-025-02219-w