Vaccines 2026

The novel oral polio vaccine type 2 (nOPV2) was widely regarded as a major advance in global polio eradication efforts. The vaccine strain was engineered to enhance genetic stability and reduce the likelihood of reversion to neurovirulence. However, a recent study published in Nature Microbiology demonstrates that, under specific conditions, even these advanced safeguards can be circumvented through viral recombination.
The study reports the isolation of a “double recombinant” poliovirus from environmental samples collected in Uganda. This variant originated from the nOPV2 vaccine strain but underwent two distinct genetic recombination events with other members of Enterovirus species C. As a result of this genetic reshuffling, the virus regained a neurovirulent phenotype. The isolate was classified as a high-risk “Category 2” variant, indicating a complete loss of the engineered attenuation.
This finding underscores an important limitation of live-attenuated poliovirus vaccines. Although nOPV2 substantially reduces the risk of vaccine-derived outbreaks compared with the original Sabin strain, it is not fully resistant to recombination in natural settings. The study reinforces the prevailing view that the long-term achievement of global polio eradication will ultimately require exclusive reliance on inactivated polio vaccines (IPV).